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/plugins/kuaidaili.py

@@ -9,6 +9,7 @@ VALID_PROTOCOLS = ("http", "https", "socks4", "socks5")
 
 
 class KuaiDaiLiPlugin(BaseHTTPPlugin):
+    default_config = {"max_pages": 5}
     name = "kuaidaili"
     display_name = "快代理"
     description = "从快代理网站爬取免费代理"
@@ -45,5 +46,5 @@ class KuaiDaiLiPlugin(BaseHTTPPlugin):
                         results.append(ProxyRaw(ip, int(port), protocol))
 
         if results:
-            logger.info(f"{self.display_name} 解析完成，获得 {len(results)} 个潜在代理")
+            logger.info(f"{self.display_name} 解析完成，获取 {len(results)} 个潜在代理")
         return results