refactor: 彻底消除硬编码 qq — 平台标识统一为 obv11

- PlatformName() 返回 "obv11"
- platformFormats key: "obv11"
- 所有 platform == "qq" 检查 → "obv11"
- session prefix: platform_qq_ → platform_obv11_
- env var PLATFORM_CHANNELS: obv11:group:xxx
- ethend 平台标识同步更新
- 注释和测试用例同步

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

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

@@ -64,7 +64,7 @@ func NewAdapter(configID, configName, mode, port, accessToken, remoteURL string,
 	}
 }
 
-func (a *Adapter) PlatformName() string   { return "qq" }
+func (a *Adapter) PlatformName() string   { return "obv11" }
 func (a *Adapter) ConfigID() string      { return a.configID }
 func (a *Adapter) ConfigName() string    { return a.configName }
 func (a *Adapter) SendIntervalMs() int   { return a.sendIntervalMs }
@@ -391,7 +391,7 @@ func (a *Adapter) ToUnified(rawMessage interface{}) (*bridge.UnifiedMessage, err
 	return &bridge.UnifiedMessage{
 		SenderID:    senderID,
 		SenderName:  senderName,
-		Platform:    "qq",
+		Platform:    "obv11",
 		ChannelID:   channelID,
 		ChannelType: channelType,
 		Content:     content,
@@ -442,7 +442,7 @@ func (a *Adapter) noticeToUnified(msg *OBv11Message) (*bridge.UnifiedMessage, er
 	return &bridge.UnifiedMessage{
 		SenderID:    senderID,
 		SenderName:  senderName,
-		Platform:    "qq",
+		Platform:    "obv11",
 		ChannelID:   channelID,
 		ChannelType: channelType,
 		Content:     content,