Tabbed export: video, audio, transcript, and subtitles

[wassgha]

Summary

Revisits the unmerged transcript export work from #29, but folds everything into the existing Export dialog as tabs instead of a separate transcript toolbar button.

Export tabs

• Video — current ffmpeg cut/concat flow, plus format (MP4 / WebM) and resolution (Original / 720p / 1080p / 4K). Disabled for audio-only projects.
• Audio — export edited audio as M4A, MP3, or WAV (works for video projects too when an audio track exists).
• Transcript — plain text or Markdown (speaker-labeled turns, cuts removed, no timestamps).
• Subtitles — SRT, VTT, or JSON. SRT/VTT omit cuts and remap onto the edited timeline; JSON keeps the full word list for re-import (same semantics as Add SRT / VTT / JSON transcript export #29).

Implementation notes

• New lib/serializeTranscript.ts (+ tests in tests/serialize-transcript-test.ts)
• exportVideo / exportAudio accept format (and resolution for video); scale never upscales past the source
• No dedicated transcript Export control in the transcript toolbar — single export entry point

UI

Video export tab
Audio export tab
Transcript export tab
Subtitles export tab
Video tab disabled on audio project

Test plan

• npx tsx tests/serialize-transcript-test.ts
• npx tsx tests/parse-transcript-test.ts
• npm run lint (no new errors)
• Video project: Export modal shows format + resolution controls
• Audio-only project: Video tab disabled with tooltip; Audio export options work
• Transcript / Subtitles tabs show format pickers and download
• Cut words + manual trim → SRT/VTT times match shortened media; TXT/MD omit cut text
• JSON subtitle export re-imports via the existing Import transcript flow

_{To show artifacts inline, enable in settings.}

  

[wassgha]

Supersedes #29