v0.3.2 — --model flag + model preference

Added

• --model flag — pick the whisper model per run (--model small). Precedence:
  --model > AUDIO_TLDR_MODEL env > default. Bare names are mapped per backend (mlx gets
  the mlx-community/whisper- prefix automatically; whisper--prefixed names are
  normalized; a full HF repo path is used as-is). whisper-cpp is unaffected (file-based model)
• The cache meta.json (and the printed JSON line) now records which model produced the
  transcript
• model preference — set a standing whisper model in
  ~/.config/audio-tldr/preferences.md (model: large-v3); the agent passes it as --model.
  An explicit per-request model always wins over the preference

Changed

• Default model is large-v3-turbo on every backend — previously faster-whisper and
  openai-whisper defaulted to small. On CPU-only machines this favors quality over speed;
  pass --model small (or set AUDIO_TLDR_MODEL=small) to restore the old behavior
• Test suite grown to 53 offline unit tests (model resolution ×5)