feat: route plugin HTTP traffic through SOCKS5 proxy

Add PySocks dependency and shared src/derp/http.py module providing
proxy-aware urlopen() and build_opener() that route through
socks5h://127.0.0.1:1080. Subclassed SocksiPyHandler passes SSL
context through to HTTPS connections.

Swapped 14 external-facing plugins to use the proxied helpers.
Local-only traffic (SearXNG, raw DNS/TLS sockets) stays direct.
Updated test mocks in test_twitch and test_alert accordingly.

plugins/exploitdb.py

@@ -7,6 +7,7 @@ import logging
 import time
 from pathlib import Path
 
+from derp.http import urlopen as _urlopen
 from derp.plugin import command
 
 log = logging.getLogger(__name__)
@@ -85,7 +86,7 @@ async def _download_csv() -> tuple[int, str]:
 
     def _fetch():
         req = urllib.request.Request(_CSV_URL, headers={"User-Agent": "derp-bot"})
-        with urllib.request.urlopen(req, timeout=60) as resp:  # noqa: S310
+        with _urlopen(req, timeout=60) as resp:
             return resp.read()
 
     try: