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>

docs/CHEATSHEET.md

@@ -69,6 +69,19 @@ Code, plugins, config, and data are bind-mounted. No rebuild needed for
 code changes -- restart the container or use `!reload` for plugins.
 Rebuild only when `requirements.txt` or `Containerfile` change.
 
+## Profiling
+
+```bash
+tools/profile                        # Top 30 by cumulative time
+tools/profile -s tottime -n 20       # Top 20 by total time
+tools/profile -f mumble              # Filter to mumble functions
+tools/profile -c -f stream_audio     # Who calls stream_audio
+tools/profile data/old.prof          # Analyze a specific file
+```
+
+Sort keys: `cumtime`, `tottime`, `calls`, `name`.
+Profile data written on graceful shutdown when bot runs with `--cprofile`.
+
 ## Bot Commands
 
 ```
@@ -569,6 +582,7 @@ HTML stripped on receive, escaped on send. IRC-only commands are no-ops.
 !keep                    # Keep current file + save metadata
 !kept                    # List kept files with metadata
 !kept clear              # Delete all kept files + metadata
+!kept repair             # Re-download missing kept files
 !duck                    # Show ducking status
 !duck on                 # Enable voice ducking
 !duck off                # Disable voice ducking