feat: add version comparison (A2) and annotation system (A3)
A2 — Version Comparison:
- 4 comparison modes: side-by-side, A-B wipe slider, overlay with
opacity, toggle with crossfade
- Synced zoom/pan across all modes
- Revision selectors for left/right image
- Keyboard shortcuts: 1-4 switch modes, Escape exits
A3 — Annotations:
- SVG overlay with 7 annotation types: rectangle, ellipse, arrow,
freehand, text, pin, screenshot paste (Cmd+V)
- All annotations anchored to image coordinates (accurate at any zoom)
- Annotation model added to Prisma schema (requires db push)
- CRUD API routes at /api/revisions/[id]/annotations
- Annotations linked to comments (transactional create)
- Screenshot callouts: draggable, resizable with corner handles
- Undo/redo stack, color picker, visibility toggle
- Floating toolbar with backdrop blur
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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