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/adapter.go

@@ -20,5 +20,11 @@ type PlatformAdapter interface {
 	HealthCheck() error
 }
 
+// ProactiveSender is an optional interface for adapters that can
+// proactively send messages (e.g., QQ bot sending without prior request).
+type ProactiveSender interface {
+	SendProactive(chatType string, userID, groupID int64, content string) error
+}
+
 // MessageHandler receives unified messages from adapters for processing.
 type MessageHandler func(msg *UnifiedMessage) (*UnifiedResponse, error)