feat: QQ主动消息管道 + 戳一戳事件 + thinker提示词优化

- ProactiveTarget 结构体 + QQ目标正则解析（extractProactiveMessage 返回双值）
- storeThought 双路推送：platform消息 → platformMessagePusher，web消息 → messagePusher
- platform-bridge: SendProactive接口 + ProactiveSender + /api/v1/internal/send-proactive端点
- QQ戳一戳/notice事件 → noticeToUnified → ContentType "action"
- thinker提示词注入QQ频道上下文：群名称(群号)、活跃时间、trigger-aware引导
- SetBotUID/SetPlatformMessagePusher/AddOrUpdatePlatformChannel 方法
- ai-core source 增加 BotUID/GroupName，platform-bridge source 增加 bot_uid/group_name
- 支持 [CQ:at,qq=xxx] @提及标签自动拼接

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

backend/platform-bridge/internal/bridge/router.go

@@ -186,6 +186,20 @@ func (r *PlatformRouter) SendResponse(response *UnifiedResponse) ([]PlatformMess
 	return a.FromUnified(response)
 }
 
+// SendProactive sends a proactive message through a platform adapter that supports it.
+// Returns an error if the adapter doesn't support proactive sending or the send fails.
+func (r *PlatformRouter) SendProactive(adapterName, chatType string, userID, groupID int64, content string) error {
+	a, err := r.GetAdapter(adapterName)
+	if err != nil {
+		return err
+	}
+	sender, ok := a.(ProactiveSender)
+	if !ok {
+		return fmt.Errorf("adapter %s does not support proactive sending", adapterName)
+	}
+	return sender.SendProactive(chatType, userID, groupID, content)
+}
+
 func (r *PlatformRouter) platformHints(platform string) PlatformHints {
 	cap := PlatformCapabilities{}
 	if a, err := r.GetAdapter(platform); err == nil {