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.

pyproject.toml

@@ -10,6 +10,7 @@ requires-python = ">=3.11"
 license = "MIT"
 dependencies = [
     "maxminddb>=2.0",
+    "PySocks>=1.7.1",
 ]
 
 [project.scripts]