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>

.env.example

@@ -40,7 +40,7 @@ PROACTIVE_MSG_MIN_GAP_SEC=1800
 PLATFORM_CHANNELS=qq:group:群号
 PLATFORM_THINK_INTERVAL_SEC=600
 # --- 平台桥接 ---
-PLATFORM_BRIDGE_URL=http://localhost:8082
+PLATFORM_BRIDGE_URL=http://localhost:8095
 
 # ========== 后端微服务地址 ==========
 GATEWAY_URL=http://localhost:8080