Add REST endpoints and frontend wiring for per-language project actions:
- POST /api/workspace/{project}/translation/{lang}/queue — queue translation
- POST /api/workspace/{project}/audio/{lang}/queue — queue audio generation
- GET/POST /api/workspace/{project}/format/{lang} — format metadata (EPUB/PDF)
- GET /api/workspace/{project}/review/{lang}/chapters/{chapter} — utterance review
- GET/POST /api/workspace/{project}/front-matter/{lang} — front matter editor
- GET /api/workspace/{project}/chapters/{lang} — chapter list
- GET /api/workspace/{project}/chapter-content/{lang}/{chapter} — chapter text
Frontend fixes:
- Review page shows per-language text (English source, Chinese translation, etc.)
- Non-translated languages show 'Queue translation' button only
- Speaker data from English source matched by paragraph ID
- UmbraAudio column layout: Speaker, Variation, Text, Actions
- Chapter tree in left sidebar: Front matter, Back matter, Body
- Audio Format label at top of sidebar
- Pandoc formatting toolbar for front matter text editing
