feat: Phase 8 - VFX 和 AI 打赏反应系统

- Unity: 添加 VFXManager 实现金币雨和爱心爆炸特效
- Unity: NetworkManager 支持 GiftEffect 事件
- Unity: AgentVisual 支持自定义时长的 SpeechBubble
- Backend: LLMService 支持生成个性化感谢语
- Backend: Engine 统一处理礼物逻辑 (handle_gift)
- Backend: TwitchBot 接入新的礼物处理流程

unity-client/Assets/Scripts/Visual/VFXManager.cs

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+using UnityEngine;
+
+namespace TheIsland.Visual
+{
+    /// <summary>
+    /// Singleton VFX Manager for handling particle effects.
+    /// Creates procedural particle systems for gift effects.
+    /// </summary>
+    public class VFXManager : MonoBehaviour
+    {
+        #region Singleton
+        private static VFXManager _instance;
+        public static VFXManager Instance
+        {
+            get
+            {
+                if (_instance == null)
+                {
+                    _instance = FindFirstObjectByType<VFXManager>();
+                    if (_instance == null)
+                    {
+                        var go = new GameObject("VFXManager");
+                        _instance = go.AddComponent<VFXManager>();
+                    }
+                }
+                return _instance;
+            }
+        }
+        #endregion
+
+        #region Settings
+        [Header("Gold Rain Settings")]
+        [SerializeField] private Color goldColor = new Color(1f, 0.84f, 0f); // Gold
+        [SerializeField] private int goldParticleCount = 50;
+        [SerializeField] private float goldDuration = 2f;
+
+        [Header("Heart Explosion Settings")]
+        [SerializeField] private Color heartColor = new Color(1f, 0.2f, 0.3f); // Red/Pink
+        [SerializeField] private int heartParticleCount = 30;
+        [SerializeField] private float heartDuration = 1.5f;
+
+        [Header("General Settings")]
+        [SerializeField] private float effectScale = 1f;
+        #endregion
+
+        #region Unity Lifecycle
+        private void Awake()
+        {
+            if (_instance != null && _instance != this)
+            {
+                Destroy(gameObject);
+                return;
+            }
+            _instance = this;
+        }
+        #endregion
+
+        #region Public Methods
+        /// <summary>
+        /// Play gold coin rain effect at position.
+        /// Used for Bits donations.
+        /// </summary>
+        public void PlayGoldRain(Vector3 position)
+        {
+            Debug.Log($"[VFXManager] Playing Gold Rain at {position}");
+            var ps = CreateGoldRainSystem(position);
+            ps.Play();
+            Destroy(ps.gameObject, goldDuration + 0.5f);
+        }
+
+        /// <summary>
+        /// Play heart explosion effect at position.
+        /// Used for subscription/heart gifts.
+        /// </summary>
+        public void PlayHeartExplosion(Vector3 position)
+        {
+            Debug.Log($"[VFXManager] Playing Heart Explosion at {position}");
+            var ps = CreateHeartExplosionSystem(position);
+            ps.Play();
+            Destroy(ps.gameObject, heartDuration + 0.5f);
+        }
+
+        /// <summary>
+        /// Play an effect by type name.
+        /// </summary>
+        public void PlayEffect(string effectType, Vector3 position)
+        {
+            switch (effectType.ToLower())
+            {
+                case "bits":
+                case "gold":
+                case "goldrain":
+                    PlayGoldRain(position);
+                    break;
+                case "heart":
+                case "hearts":
+                case "sub":
+                case "subscription":
+                    PlayHeartExplosion(position);
+                    break;
+                default:
+                    // Default to gold rain
+                    PlayGoldRain(position);
+                    break;
+            }
+        }
+        #endregion
+
+        #region Particle System Creation
+        /// <summary>
+        /// Create a procedural gold coin rain particle system.
+        /// </summary>
+        private ParticleSystem CreateGoldRainSystem(Vector3 position)
+        {
+            GameObject go = new GameObject("GoldRain_VFX");
+            go.transform.position = position + Vector3.up * 3f; // Start above
+            
+            ParticleSystem ps = go.AddComponent<ParticleSystem>();
+            var main = ps.main;
+            main.loop = false;
+            main.duration = goldDuration;
+            main.startLifetime = 1.5f;
+            main.startSpeed = 2f;
+            main.startSize = 0.15f * effectScale;
+            main.startColor = goldColor;
+            main.gravityModifier = 1f;
+            main.maxParticles = goldParticleCount;
+            main.simulationSpace = ParticleSystemSimulationSpace.World;
+
+            // Emission - burst at start
+            var emission = ps.emission;
+            emission.enabled = true;
+            emission.rateOverTime = 0;
+            emission.SetBursts(new ParticleSystem.Burst[]
+            {
+                new ParticleSystem.Burst(0f, goldParticleCount)
+            });
+
+            // Shape - spread from point
+            var shape = ps.shape;
+            shape.enabled = true;
+            shape.shapeType = ParticleSystemShapeType.Circle;
+            shape.radius = 1f * effectScale;
+
+            // Size over lifetime - shrink slightly
+            var sizeOverLifetime = ps.sizeOverLifetime;
+            sizeOverLifetime.enabled = true;
+            AnimationCurve sizeCurve = new AnimationCurve();
+            sizeCurve.AddKey(0f, 1f);
+            sizeCurve.AddKey(1f, 0.5f);
+            sizeOverLifetime.size = new ParticleSystem.MinMaxCurve(1f, sizeCurve);
+
+            // Color over lifetime - fade out
+            var colorOverLifetime = ps.colorOverLifetime;
+            colorOverLifetime.enabled = true;
+            Gradient gradient = new Gradient();
+            gradient.SetKeys(
+                new GradientColorKey[] { 
+                    new GradientColorKey(goldColor, 0f), 
+                    new GradientColorKey(goldColor, 0.7f) 
+                },
+                new GradientAlphaKey[] { 
+                    new GradientAlphaKey(1f, 0f), 
+                    new GradientAlphaKey(1f, 0.5f), 
+                    new GradientAlphaKey(0f, 1f) 
+                }
+            );
+            colorOverLifetime.color = gradient;
+
+            // Rotation - spin
+            var rotationOverLifetime = ps.rotationOverLifetime;
+            rotationOverLifetime.enabled = true;
+            rotationOverLifetime.z = new ParticleSystem.MinMaxCurve(-180f, 180f);
+
+            // Renderer - use default sprite
+            var renderer = go.GetComponent<ParticleSystemRenderer>();
+            renderer.renderMode = ParticleSystemRenderMode.Billboard;
+            renderer.material = CreateParticleMaterial(goldColor);
+
+            return ps;
+        }
+
+        /// <summary>
+        /// Create a procedural heart explosion particle system.
+        /// </summary>
+        private ParticleSystem CreateHeartExplosionSystem(Vector3 position)
+        {
+            GameObject go = new GameObject("HeartExplosion_VFX");
+            go.transform.position = position + Vector3.up * 1.5f;
+            
+            ParticleSystem ps = go.AddComponent<ParticleSystem>();
+            var main = ps.main;
+            main.loop = false;
+            main.duration = heartDuration;
+            main.startLifetime = 1.2f;
+            main.startSpeed = new ParticleSystem.MinMaxCurve(3f, 5f);
+            main.startSize = 0.2f * effectScale;
+            main.startColor = heartColor;
+            main.gravityModifier = -0.3f; // Float up slightly
+            main.maxParticles = heartParticleCount;
+            main.simulationSpace = ParticleSystemSimulationSpace.World;
+
+            // Emission - burst at start
+            var emission = ps.emission;
+            emission.enabled = true;
+            emission.rateOverTime = 0;
+            emission.SetBursts(new ParticleSystem.Burst[]
+            {
+                new ParticleSystem.Burst(0f, heartParticleCount)
+            });
+
+            // Shape - explode outwards from sphere
+            var shape = ps.shape;
+            shape.enabled = true;
+            shape.shapeType = ParticleSystemShapeType.Sphere;
+            shape.radius = 0.3f * effectScale;
+
+            // Size over lifetime - grow then shrink
+            var sizeOverLifetime = ps.sizeOverLifetime;
+            sizeOverLifetime.enabled = true;
+            AnimationCurve sizeCurve = new AnimationCurve();
+            sizeCurve.AddKey(0f, 0.5f);
+            sizeCurve.AddKey(0.3f, 1.2f);
+            sizeCurve.AddKey(1f, 0.2f);
+            sizeOverLifetime.size = new ParticleSystem.MinMaxCurve(1f, sizeCurve);
+
+            // Color over lifetime - vibrant to fade
+            var colorOverLifetime = ps.colorOverLifetime;
+            colorOverLifetime.enabled = true;
+            Gradient gradient = new Gradient();
+            gradient.SetKeys(
+                new GradientColorKey[] { 
+                    new GradientColorKey(heartColor, 0f), 
+                    new GradientColorKey(new Color(1f, 0.5f, 0.6f), 0.5f),
+                    new GradientColorKey(heartColor, 1f) 
+                },
+                new GradientAlphaKey[] { 
+                    new GradientAlphaKey(1f, 0f), 
+                    new GradientAlphaKey(1f, 0.4f), 
+                    new GradientAlphaKey(0f, 1f) 
+                }
+            );
+            colorOverLifetime.color = gradient;
+
+            // Rotation - gentle spin
+            var rotationOverLifetime = ps.rotationOverLifetime;
+            rotationOverLifetime.enabled = true;
+            rotationOverLifetime.z = new ParticleSystem.MinMaxCurve(-90f, 90f);
+
+            // Renderer
+            var renderer = go.GetComponent<ParticleSystemRenderer>();
+            renderer.renderMode = ParticleSystemRenderMode.Billboard;
+            renderer.material = CreateParticleMaterial(heartColor);
+
+            return ps;
+        }
+
+        /// <summary>
+        /// Create a simple additive particle material.
+        /// </summary>
+        private Material CreateParticleMaterial(Color color)
+        {
+            // Use a built-in shader that works well for particles
+            Shader shader = Shader.Find("Particles/Standard Unlit");
+            if (shader == null)
+            {
+                shader = Shader.Find("Unlit/Color");
+            }
+
+            Material mat = new Material(shader);
+            mat.color = color;
+            
+            // Enable additive blending for glow effect
+            if (shader.name.Contains("Particles"))
+            {
+                mat.SetFloat("_Mode", 2); // Additive
+                mat.SetInt("_SrcBlend", (int)UnityEngine.Rendering.BlendMode.SrcAlpha);
+                mat.SetInt("_DstBlend", (int)UnityEngine.Rendering.BlendMode.One);
+            }
+
+            // Use default particle texture
+            Texture2D particleTex = CreateDefaultParticleTexture();
+            mat.mainTexture = particleTex;
+
+            return mat;
+        }
+
+        /// <summary>
+        /// Create a simple circular particle texture procedurally.
+        /// </summary>
+        private Texture2D CreateDefaultParticleTexture()
+        {
+            int size = 32;
+            Texture2D tex = new Texture2D(size, size, TextureFormat.RGBA32, false);
+            Color[] pixels = new Color[size * size];
+            
+            float center = size / 2f;
+            float radius = size / 2f - 1;
+
+            for (int y = 0; y < size; y++)
+            {
+                for (int x = 0; x < size; x++)
+                {
+                    float dist = Vector2.Distance(new Vector2(x, y), new Vector2(center, center));
+                    float alpha = Mathf.Clamp01(1f - (dist / radius));
+                    alpha = alpha * alpha; // Softer falloff
+                    pixels[y * size + x] = new Color(1f, 1f, 1f, alpha);
+                }
+            }
+
+            tex.SetPixels(pixels);
+            tex.Apply();
+            return tex;
+        }
+        #endregion
+    }
+}

unity-client/Assets/Scripts/Visual/VFXManager.cs.meta

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+fileFormatVersion: 2
+guid: c07bfc9fddc8347ea826abf2adc4d44c