Add "Render Selected" for video generation

[davior]

Summary

Implement automatic detection and rendering of selected text in video generation. When a user highlights a portion of their note, the video renderer now uses only that selection instead of the entire note.

Key features:

• Transparent selection detection: Uses existing getEditorSelectionMarkdown() function from AI assistant
• Automatic fallback: Single "Video (MP4)" button works with or without selection
• Smart diagram filtering: Only rasterizes diagrams within selected blocks (faster for large notes)
• Accurate estimates: /video/estimate endpoint respects selected content for accurate segment/duration predictions

Changes

Frontend

• EditorView.tsx: Detect selection, filter diagram rasterization to selected blocks, pass selectedContent through VideoGenModal
• VideoGenModal.tsx: Accept optional selectedContent prop, pass to render function
• activity.ts: Thread selectedContent through startVideo() call
• videoGen.ts: Include selected_content in API request payload

Backend

• schemas.py: Add selected_content: Optional[str] to VideoRenderRequest
• models.py: Add selected_content: Optional[str] column to VideoRenderJob
• routers/video.py: Store selected_content in job, use in estimate endpoint
• worker.py: Use job.selected_content if present, else fetch full note
• database.py: Migration to add nullable selected_content column to video_render_jobs

Testing

• Render full note (no selection) → works as before
• Highlight a section → VideoGenModal shows estimate for selection only
• Estimate reflects selection scope (fewer segments, shorter duration)
• Click "Preview" or "Generate" → video renders only selected content
• Output video duration is noticeably shorter than full-note render
• Diagrams outside selection are skipped during rasterization

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Generated with Claude Code

https://claude.ai/code/session_01KrPcbycrTZrrThFR2a23Yz

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Generated by Claude Code

[davior]

Fixed TypeScript compilation error in the initial commit. The issue was that the startVideo() function signature in the activity store interface wasn't updated to accept the new selectedContent parameter. The implementation accepted it, but the type definition didn't, causing TS2554 error at EditorView.tsx:993.

Fix: Updated the ActivityState.startVideo type signature to include the optional selectedContent?: string parameter.

Commit: 2b97dde

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Generated by Claude Code

[davior]

✅ CI is now passing!

Both checks completed successfully:

• ✅ Backend (pytest)
• ✅ Frontend (vitest + build)

The TypeScript fix resolved the compilation error. The PR is now ready for code review and testing.

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Generated by Claude Code