fix(crawl): throttle concurrent CrawlJobs and relax fpw/proxyscrape HTTP

- CrawlJob waits on crawl_slot before JobExecutor semaphore so crawl-all does not fill slots while queued
- BaseHTTPPlugin: longer connect budget for slow international links
- proxyscrape: jsDelivr mirror + longer GitHub/API phases
- fpw_*: higher timeouts/retries; lower internal concurrency on heavy multi-URL plugins

Made-with: Cursor

app/plugins/base.py

@@ -52,7 +52,8 @@ class BaseHTTPPlugin(BaseCrawlerPlugin):
     def _http_timeout(seconds: float) -> httpx.Timeout:
         """连接阶段单独收紧，避免 AsyncClient 在部分环境下长时间卡在 connect。"""
         t = max(2.0, float(seconds))
-        c = min(6.0, max(3.0, t * 0.35))
+        # 国际链路 / 批量爬取时 connect 过短易集体超时
+        c = min(12.0, max(4.0, t * 0.4))
         return httpx.Timeout(t, connect=c)
 
     @staticmethod