fix: QQ发送消息中文乱码 — SendMessage 显式设置 auto_escape=false

NapCat 在 auto_escape 未传时默认走 escape 模式，导致 UTF-8 中文被当 CQ 码处理

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

backend/platform-bridge/internal/adapter/qq/adapter.go

@@ -486,6 +486,7 @@ func (a *Adapter) SendMessage(msgType string, userID, groupID int64, content str
 			UserID:      userID,
 			GroupID:     groupID,
 			Message:     content,
+			AutoEscape:  false,
 		},
 		Echo: fmt.Sprintf("echo_%d", time.Now().UnixNano()),
 	}