feat: 频道自动发现 — platform-bridge定时刷新频道路由 + ai-core周期同步

platform-bridge:
- QQ adapter: FetchGroups/FetchFriends 从NapCat API获取
- ChannelLister接口 + ChannelInfo结构体
- GET /api/v1/channels 端点 + cachedChannels缓存
- StartChannelRefresh 每10分钟自动刷新

ai-core:
- channel_sync.go: 每5分钟从platform-bridge拉取频道
- 自动更新thinker的platformChannels + botUIDs
- 不再依赖PLATFORM_CHANNELS环境变量手动配置

修复:
- SendMessage显式设AutoEscape:false
- PLATFORM_BRIDGE_URL默认端口8082→8095
- OBv11Params.AutoEscape去掉omitempty

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

backend/ai-core/cmd/main.go

@@ -389,7 +389,7 @@ func main() {
 		log.Printf("[主动消息] 推送已启用 (Gateway=%s)", gatewayURL)
 
 		// 设置平台主动消息推送回调（调用 Platform Bridge 内部 API）
-		platformBridgeURL := getEnv("PLATFORM_BRIDGE_URL", "http://localhost:8082")
+		platformBridgeURL := getEnv("PLATFORM_BRIDGE_URL", "http://localhost:8095")
 		thinker.SetPlatformMessagePusher(func(target background.ProactiveTarget, message string) {
 			reqBody, _ := json.Marshal(map[string]string{
 				"platform":   target.Platform,
@@ -418,6 +418,7 @@ func main() {
 			}
 		})
 		log.Printf("[主动消息] 平台推送已启用 (PlatformBridge=%s)", platformBridgeURL)
+		go syncPlatformChannels(thinker, platformBridgeURL, internalToken)
 	} else {
 		log.Println("[主动消息] 未配置 INTERNAL_SERVICE_TOKEN，主动消息推送已禁用")
 	}