fix: buildThinkingUserPrompt嵌套锁死锁 + 管理员群聊路由优化

- thinker.go:1662/1762 defer t.muUnlock→立即解锁，消除buildThinkingUserPrompt自死锁
  (1662持锁后1762再Lock→同goroutine自死锁→23h锁泄露→3769 goroutine泄漏)
- platform-bridge: 管理员在群里@别人走group_ambient而非normal，避免频繁插嘴

backend/platform-bridge/cmd/main.go

@@ -211,8 +211,16 @@ func main() {
 			response = &bridge.UnifiedResponse{Messages: []bridge.ResponseMessage{{DisplayType: "silent"}}, Platform: msg.Platform}
 
 		case isAdmin:
-			msg.RouteType = "normal"
-			response, routeErr = forwardToAICore(cfg, msg, "text", chatUserID, groupSessionID, imageURLs, videoURLs, voiceURLs, isAdmin)
+			// 管理员在群里@别人(非bot)时，用 group_ambient 避免昔涟频繁插嘴
+			if msg.ChannelType == "group" && !isBotMentioned {
+				msg.RouteType = "group_ambient"
+				namespace := buildMemoryNamespace(msg.Platform, msg.ChannelType, msg.ChannelID)
+				fireSilent(namespace, imageURLs, videoURLs, voiceURLs)
+				response, routeErr = forwardToAICore(cfg, msg, "group_ambient", chatUserID, groupSessionID, imageURLs, videoURLs, voiceURLs, isAdmin)
+			} else {
+				msg.RouteType = "normal"
+				response, routeErr = forwardToAICore(cfg, msg, "text", chatUserID, groupSessionID, imageURLs, videoURLs, voiceURLs, isAdmin)
+			}
 
 		case isBotMentioned:
 			msg.RouteType = "normal"