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/platform-bridge/internal/bridge/adapter.go

@@ -26,5 +26,19 @@ type ProactiveSender interface {
 	SendProactive(chatType string, userID, groupID int64, content string) error
 }
 
+// ChannelInfo describes a known chat channel (group or private).
+type ChannelInfo struct {
+	Platform    string `json:"platform"`
+	ChannelType string `json:"channel_type"` // "group", "private"
+	ChannelID   string `json:"channel_id"`
+	ChannelName string `json:"channel_name,omitempty"`
+}
+
+// ChannelLister is an optional interface for adapters that can enumerate
+// their channels (groups and friends) from the platform API.
+type ChannelLister interface {
+	ListChannels() []ChannelInfo
+}
+
 // MessageHandler receives unified messages from adapters for processing.
 type MessageHandler func(msg *UnifiedMessage) (*UnifiedResponse, error)