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

backend/app/main.py

@@ -140,6 +140,13 @@ async def websocket_endpoint(websocket: WebSocket):
                 text = message.payload.get("message", "")
                 await engine.process_comment(user, text)
 
+            # Handle test gift action
+            elif message.action == "test_gift":
+                user = message.payload.get("user", "TestUser")
+                bits = int(message.payload.get("bits", 100))
+                # Trigger handle_gift in engine
+                await engine.handle_gift(user, bits, "bits")
+
     except WebSocketDisconnect:
         manager.disconnect(websocket)
     except Exception as e: