refactor(backend): optimize database safety, validator performance, and scheduler concurrency

- Fix SQL injection risks in proxy_repo and task_repo
- Atomic acquire_pending with UPDATE ... RETURNING
- Reuse aiohttp ClientSession in ValidatorService
- Replace polling with asyncio.Event in SchedulerService
- Optimize ValidationQueue.drain with asyncio.Condition
- Concurrent plugin crawling with asyncio.gather
- Unify ProxyRaw model import path
- Fix test baseline and remove tracked __pycache__ files

app/core/plugin_system/base.py

@@ -1,20 +1,7 @@
 """插件基类 - 所有爬虫插件必须继承此基类"""
 from abc import ABC, abstractmethod
-from dataclasses import dataclass
 from typing import List, Dict, Any
-
-
-@dataclass
-class ProxyRaw:
-    """爬虫产出的原始代理数据"""
-    ip: str
-    port: int
-    protocol: str = "http"
-
-    def __post_init__(self):
-        self.protocol = self.protocol.lower().strip()
-        if self.protocol not in ("http", "https", "socks4", "socks5"):
-            self.protocol = "http"
+from app.models.domain import ProxyRaw
 
 
 class BaseCrawlerPlugin(ABC):