feat(backend): setup wizard router, translation engines, export options, client-disconnect handling
- Add setup router (backend/api/routers/setup.py) for first-run wizard:
system checks, engine probes, model downloads with progress
- Add translation engines service with pluggable backends
- Add utils/hf_progress for HuggingFace download progress streaming
- Add PyInstaller runtime hooks (numpy compat, torch compiler disable)
- Global exception handler short-circuits h11 LocalProtocolError and
Starlette ClientDisconnect with HTTP 499 to silence noisy stack traces
when users scrub or cancel video mid-stream
- /dub/download-mp3 accepts bitrate query param (clamped 64–320kbps)
- Refactor ASR/TTS backends, dub pipeline, engine management
- Update backend.spec for PyInstaller packaging
- Bump pyproject version to 0.2.0; refresh uv.lock
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
