STTService._transcribe_local writes the audio to a NamedTemporaryFile
(delete=False) and only unlinks it on the success path, before the except.
If model.transcribe() raises (corrupt audio, model/runtime error, etc.) the
function logs, returns None, and leaves the .webm temp file behind — so
every failed local transcription leaks a file in the system temp dir.
Initialize tmp_path = None up front and move the unlink into a finally
block so the temp file is cleaned up whether transcription succeeds or
raises.
tests/test_stt_leak.py stubs the whisper model to raise during transcribe,
runs _transcribe_local, and asserts it returns None and leaves no new .webm
file in the temp dir. Fails before this change.
faster-whisper runs on CTranslate2, not torch, but _get_whisper()
imported torch (only to check cuda availability) inside the same try as
the faster-whisper import. on a torch-less machine that raised
ImportError and reported the misleading 'faster-whisper not installed'
even when it was installed, so local mic transcription silently failed.
probe torch separately and optionally: present -> cuda, absent -> cpu.
also declare faster-whisper in requirements-optional.txt (torch stays an
optional extra for gpu).
