feat: add Unity 6 client with 2.5D visual system

Unity client features:
- WebSocket connection via NativeWebSocket
- 2.5D agent visuals with programmatic placeholder sprites
- Billboard system for sprites and UI elements
- Floating UI panels (name, HP, energy bars)
- Speech bubble system with pop-in animation
- RTS-style camera controller (WASD + scroll zoom)
- Editor tools for prefab creation and scene setup

Scripts:
- NetworkManager: WebSocket singleton
- GameManager: Agent spawning and event handling
- AgentVisual: 2.5D sprite and UI creation
- Billboard: Camera-facing behavior
- SpeechBubble: Animated dialogue display
- CameraController: RTS camera with UI input detection
- UIManager: HUD and command input

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

unity-client/Assets/TextMesh Pro/Examples & Extras/Scripts/TMP_DigitValidator.cs

@@ -0,0 +1,27 @@
+using UnityEngine;
+using System;
+
+
+namespace TMPro
+{
+    /// <summary>
+    /// EXample of a Custom Character Input Validator to only allow digits from 0 to 9.
+    /// </summary>
+    [Serializable]
+    //[CreateAssetMenu(fileName = "InputValidator - Digits.asset", menuName = "TextMeshPro/Input Validators/Digits", order = 100)]
+    public class TMP_DigitValidator : TMP_InputValidator
+    {
+        // Custom text input validation function
+        public override char Validate(ref string text, ref int pos, char ch)
+        {
+            if (ch >= '0' && ch <= '9')
+            {
+                text += ch;
+                pos += 1;
+                return ch;
+            }
+
+            return (char)0;
+        }
+    }
+}