feat: make SOCKS5 proxy configurable per adapter

Add `proxy` config option to server (IRC), teams, telegram, and mumble
sections. IRC defaults to false (preserving current direct-connect
behavior); all others default to true. The `derp.http` module now
accepts `proxy=True/False` on urlopen, create_connection,
open_connection, and build_opener -- when false, uses stdlib directly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_irc.py

@@ -1,6 +1,12 @@
 """Tests for IRC message parsing and formatting."""
 
-from derp.irc import _parse_tags, _unescape_tag_value, format_msg, parse
+from derp.irc import (
+    IRCConnection,
+    _parse_tags,
+    _unescape_tag_value,
+    format_msg,
+    parse,
+)
 
 
 class TestParse:
@@ -142,3 +148,19 @@ class TestFormat:
         # No space in tail, not starting with colon, head exists -> no colon
         result = format_msg("MODE", "#ch", "+o", "nick")
         assert result == "MODE #ch +o nick"
+
+
+class TestIRCConnectionProxy:
+    """IRCConnection proxy flag tests."""
+
+    def test_proxy_default_false(self):
+        conn = IRCConnection("irc.example.com", 6697)
+        assert conn.proxy is False
+
+    def test_proxy_enabled(self):
+        conn = IRCConnection("irc.example.com", 6697, proxy=True)
+        assert conn.proxy is True
+
+    def test_proxy_disabled(self):
+        conn = IRCConnection("irc.example.com", 6697, proxy=False)
+        assert conn.proxy is False