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/core/db.py

@@ -77,6 +77,13 @@ async def init_db():
             await db.execute("ALTER TABLE plugin_settings ADD COLUMN config_json TEXT DEFAULT '{}'")
             logger.info("Migrated: added config_json column to plugin_settings")
 
+        # 迁移：为旧版 plugin_settings 表增加 stats_json 列
+        try:
+            await db.execute("SELECT stats_json FROM plugin_settings LIMIT 1")
+        except Exception:
+            await db.execute("ALTER TABLE plugin_settings ADD COLUMN stats_json TEXT DEFAULT '{}'")
+            logger.info("Migrated: added stats_json column to plugin_settings")
+
         # 验证任务队列表
         await db.execute("""
             CREATE TABLE IF NOT EXISTS validation_tasks (

app/core/tasks/queue.py

@@ -56,6 +56,12 @@ class ValidationQueue:
         async with get_db() as db:
             recovered = await self.task_repo.reset_processing(db)
             pending = await self.task_repo.get_pending_count(db)
+            if pending > 1000:
+                logger.warning(f"ValidationQueue has {pending} pending tasks, cleaning up all pending tasks...")
+                await db.execute("DELETE FROM validation_tasks WHERE status = 'pending'")
+                await db.commit()
+                pending = await self.task_repo.get_pending_count(db)
+                logger.info(f"ValidationQueue cleaned up pending tasks, remaining: {pending}")
         if recovered:
             logger.info(f"ValidationQueue recovered {recovered} interrupted tasks")
         if pending: