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/handler/bridge_handler.go

@@ -180,7 +180,7 @@ func (h *BridgeHandler) sendProactive(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// Map chat type to QQ message_type
+	// Map chat type to OBv11 message_type
 	msgType := req.ChatType
 	if msgType != "private" && msgType != "group" {
 		writeJSON(w, http.StatusBadRequest, errResp("chat_type must be private or group"))
@@ -196,7 +196,7 @@ func (h *BridgeHandler) sendProactive(w http.ResponseWriter, r *http.Request) {
 		content = fmt.Sprintf("[CQ:at,qq=%s] %s", req.AtUserID, content)
 	}
 
-	// Find the adapter. For QQ, use "qq" as the default adapter name.
+	// Find the adapter. For OBv11, use the platform name as adapter name.
 	adapterName := req.Platform
 	err := h.router.SendProactive(adapterName, msgType, userID, groupID, content)
 	if err != nil {