fix: use gitleaks CLI instead of licensed action, fix lint errors

- Replace gitleaks-action (requires paid license) with direct CLI
  invocation -- same engine, no license needed
- Fix ruff I001 import sorting in voice.py and test_llm.py
- Remove unused imports: _chat_request (test_llm), Path (test_music)
- Remove unused assignment: original_spawn (test_voice)

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

tests/test_music.py

@@ -4,7 +4,6 @@ import asyncio
 import importlib.util
 import sys
 import time
-from pathlib import Path
 from unittest.mock import AsyncMock, MagicMock, patch
 
 # -- Load plugin module directly ---------------------------------------------