style: apply ruff auto-fixes across codebase

- Fix import sorting (isort) across all engine modules
- Fix SIM105 try-except-pass patterns (contextlib.suppress)
- Fix nested with statements in tests
- Fix unused loop variables

Run 'uv run pytest' to verify tests still pass.

engine/mic.py

@@ -6,8 +6,8 @@ Gracefully degrades if sounddevice/numpy are unavailable.
 import atexit
 
 try:
-    import sounddevice as _sd
     import numpy as _np
+    import sounddevice as _sd
     _HAS_MIC = True
 except Exception:
     _HAS_MIC = False