Three defects found while auditing the 'person from a video -> scene with their
voice' path.

1. camera_motion returned 500 on every request that used it.
   _apply_camera_motion() set kw['camera_motion'] unconditionally and nothing
   ever popped it, so pipe(**kw) raised TypeError — no diffusers video pipeline
   accepts that kwarg (the 'CogVideoX supports it natively' comment was wrong).
   tools/videogen.py sends the field, so that path was dead. Now the kwarg is
   passed only when the pipeline signature really takes it, otherwise the motion
   is folded into the prompt, which is the only conditioning these models have.

2. dialogs[].voice never cloned the voice it named.
   _generate_tts_for_line() loaded the profile's reference audio and then used it
   purely as a flag to force a generic voice (en-US-JennyNeural / af_sky) —
   F5-TTS was never invoked, so the selected identity was silently discarded.
   It now clones with F5-TTS when the profile has reference audio AND a
   transcript, and says why in the log when it falls back.

3. seed-vc and F5-TTS could not load their BigVGAN vocoder.
   huggingface_hub 1.x stopped forwarding proxies/resume_download to a subclass
   _from_pretrained; BigVGAN still declares them as required keyword-only args,
   so loading died with 'missing 2 required keyword-only arguments'. Pinning hub
   below 1.0 is not possible (transformers 5.x needs the new one), so
   codai/api/hub_compat.py supplies the dropped arguments for exactly the
   subclasses whose signature still requires them. This also un-breaks
   /v1/audio/convert.

Also fixed on the way:
- edge-tts never ran: get_event_loop().run_until_complete() inside an executor
  thread raises RuntimeError. In _generate_tts_for_line it was swallowed; in
  _generate_tts only ImportError was caught, so it propagated out of
  /v1/video/dub. Both now use asyncio.run() and verify the output file.
- music dub adopted a failed Seed-VC result: converted_path was assigned before
  the write succeeded, so a near-empty conversion got remixed instead of falling
  back to the F5-TTS vocal. The result is now validated before adoption.

Verified offline (live container untouched): camera_motion passes through only
to a supporting pipeline and otherwise reaches the prompt; a dialog line clones
with the profile's reference audio and transcript and refuses to clone without
one; seed-vc loads BigVGAN and converts; the music dub falls back to the full
vocal and reports the reason.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01R6iugoNeEgt9PkajKrFyq4