feat: playlist shuffle, lazy resolution, TTS ducking, kept repair

Music:
- #random URL fragment shuffles playlist tracks before enqueuing
- Lazy playlist resolution: first 10 tracks resolve immediately,
  remaining are fetched in a background task
- !kept repair re-downloads kept tracks with missing local files
- !kept shows [MISSING] marker for tracks without local files
- TTS ducking: music ducks when merlin speaks via voice peer,
  smooth restore after TTS finishes

Performance (from profiling):
- Connection pool: preload_content=True for SOCKS connection reuse
- Pool tuning: 30 pools / 8 connections (up from 20/4)
- _PooledResponse wrapper for stdlib-compatible read interface
- Iterative _extract_videos (replace 51K-deep recursion with stack)
- proxy=False for local SearXNG

Voice + multi-bot:
- Per-bot voice config lookup ([<username>.voice] in TOML)
- Mute detection: skip duck silence when all users muted
- Autoplay shuffle deck (no repeats until full cycle)
- Seek clamp to track duration (prevent seek-past-end stall)

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

tests/test_http.py

@@ -203,11 +203,15 @@ class TestUrlopen:
         pool = MagicMock()
         resp = MagicMock()
         resp.status = 200
+        resp.data = b"ok"
+        resp.reason = "OK"
+        resp.headers = {}
         pool.request.return_value = resp
         mock_pool_fn.return_value = pool
 
         result = urlopen("https://example.com/")
-        assert result is resp
+        assert result.status == 200
+        assert result.read() == b"ok"
 
     @patch.object(derp.http, "_get_pool")
     def test_context_falls_back_to_opener(self, mock_pool_fn):