fix: 修复爬虫网络层、验证队列卡死及 API 500 错误

- 修复 BaseHTTPPlugin 连接池、并发控制、异常日志、超时策略
- 修复/增强 8 个爬虫插件的稳定性和 fallback 机制
- 清理 validation_tasks 表 4 万+ pending 任务，避免队列卡死
- 修复 app/api/main.py 缺失全局 app 实例导致的 500 错误
- 提升前端 Axios 超时到 120 秒，避免请求断开
- 修复插件统计持久化和调度器生命周期问题

app/repositories/settings_repo.py

@@ -124,17 +124,55 @@ class PluginSettingsRepository:
             logger.error(f"set_config failed for {plugin_id}: {e}")
             return False
 
+    @staticmethod
+    async def get_stats(db: aiosqlite.Connection, plugin_id: str) -> Dict[str, Any]:
+        async with db.execute(
+            "SELECT stats_json FROM plugin_settings WHERE plugin_id = ?", (plugin_id,)
+        ) as cursor:
+            row = await cursor.fetchone()
+            if row and row[0]:
+                try:
+                    return json.loads(row[0])
+                except json.JSONDecodeError:
+                    return {}
+            return {}
+
+    @staticmethod
+    async def set_stats(db: aiosqlite.Connection, plugin_id: str, stats: Dict[str, Any]) -> bool:
+        try:
+            await db.execute(
+                """
+                INSERT INTO plugin_settings (plugin_id, stats_json, updated_at)
+                VALUES (?, ?, CURRENT_TIMESTAMP)
+                ON CONFLICT(plugin_id) DO UPDATE SET
+                    stats_json = excluded.stats_json,
+                    updated_at = CURRENT_TIMESTAMP
+                """,
+                (plugin_id, json.dumps(stats, ensure_ascii=False)),
+            )
+            await db.commit()
+            return True
+        except Exception as e:
+            logger.error(f"set_stats failed for {plugin_id}: {e}")
+            return False
+
     @staticmethod
     async def list_all(db: aiosqlite.Connection) -> Dict[str, Dict[str, Any]]:
         result = {}
-        async with db.execute("SELECT plugin_id, enabled, config_json FROM plugin_settings") as cursor:
+        async with db.execute("SELECT plugin_id, enabled, config_json, stats_json FROM plugin_settings") as cursor:
             rows = await cursor.fetchall()
-            for plugin_id, enabled, config_json in rows:
+            for plugin_id, enabled, config_json, stats_json in rows:
                 config = {}
                 if config_json:
                     try:
                         config = json.loads(config_json)
                     except json.JSONDecodeError:
                         pass
-                result[plugin_id] = {"enabled": bool(enabled), "config": config}
+                stats = {}
+                if stats_json:
+                    try:
+                        stats = json.loads(stats_json)
+                    except json.JSONDecodeError:
+                        pass
+                result[plugin_id] = {"enabled": bool(enabled), "config": config, "stats": stats}
         return result