feat: fpw plugins, validation/crawl perf, WS stats, test DB isolation

- Add Free_Proxy_Website-style fpw_* plugins and register them
- Per-plugin crawl timeout (crawl_timeout_seconds=120); remove global crawl_timeout setting
- Validator: fix connect vs total timeout on save; SOCKS session LRU cache; drop redundant semaphore
- Validation handler uses single DB connection; batch upsert after crawl; WorkerPool put_nowait
- Remove unused max_retries from settings API/UI; settings maintenance SQL + init_db cleanup of deprecated keys
- WebSocket dashboard stats; ProxyList pool_filter and API alignment
- POST /api/proxies/delete-one for IPv6-safe deletes; task poll stops on 404
- pytest uses PROXYPOOL_DB_PATH=db/proxies.test.sqlite so tests do not wipe production DB
- .gitignore: explicit proxies.test.sqlite patterns; fix plugin_service ValidationException import

Made-with: Cursor

app/services/dashboard_stats.py

@@ -0,0 +1,9 @@
+"""首页 / 仪表盘统计快照（供 REST 与 WebSocket 复用）"""
+from app.services.proxy_service import ProxyService
+
+
+async def get_dashboard_stats(scheduler_running: bool) -> dict:
+    proxy_service = ProxyService()
+    stats = await proxy_service.get_stats()
+    stats["scheduler_running"] = scheduler_running
+    return stats