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_llm.py

@@ -23,7 +23,6 @@ from plugins.llm import (  # noqa: E402
     _COOLDOWN,
     _MAX_HISTORY,
     _MAX_REPLY_LEN,
-    _chat_request,
     _check_cooldown,
     _extract_reply,
     _get_api_key,
@@ -35,7 +34,6 @@ from plugins.llm import (  # noqa: E402
     cmd_chat,
 )
 
-
 # -- Helpers -----------------------------------------------------------------
 
 class _FakeState: