refactor: QQ → OBv11 重命名 + 平台格式统一抽象

- 所有对外称呼从 QQ 改为 OBv11（注释/提示词/日志/配置项）
- 新增 PlatformFormat 结构体，统一管理平台消息标记格式
- defaultPlatformFormats() 注册表替代硬编码 qqTargetRe
- extractProactiveMessage 改为 Thinker 方法，遍历格式注册表匹配
- 配置项重命名: QQ_BOT_PORT → OBV11_BOT_PORT, QQBotPort → OBv11BotPort
- 标记格式: 【QQ群聊】→【OBv11群聊】、【QQ私聊】→【OBv11私聊】

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

backend/platform-bridge/internal/config/config.go

@@ -14,7 +14,7 @@ type Config struct {
 	InternalToken  string
 
 	// Platform-specific.
-	QQBotPort           string // port for QQ OBv11 reverse WebSocket
+	OBv11BotPort        string // port for OBv11 reverse WebSocket
 	TelegramToken       string // Telegram Bot API token
 	TelegramWebhookURL  string // public webhook URL for Telegram
 
@@ -34,7 +34,7 @@ func Load() *Config {
 		Env:           "development",
 		GatewayURL:    "http://localhost:8080",
 		AICoreURL:     "http://localhost:8081",
-		QQBotPort:     "8096",
+		OBv11BotPort:  "8096",
 	}
 	if v := os.Getenv("PORT"); v != "" {
 		cfg.Port = v
@@ -51,8 +51,8 @@ func Load() *Config {
 	if v := os.Getenv("INTERNAL_SERVICE_TOKEN"); v != "" {
 		cfg.InternalToken = v
 	}
-	if v := os.Getenv("QQ_BOT_PORT"); v != "" {
-		cfg.QQBotPort = v
+	if v := os.Getenv("OBV11_BOT_PORT"); v != "" {
+		cfg.OBv11BotPort = v
 	}
 	if v := os.Getenv("TELEGRAM_BOT_TOKEN"); v != "" {
 		cfg.TelegramToken = v