- AnnotationShape.svelte: renders a single annotation as either a
rectangle or a polygon-clipped div (via CSS clip-path: polygon())
- AnnotationLayer.svelte: refactored to delegate rendering to
AnnotationShape, keeping draw logic and hover state management
- Annotation type: added optional polygon field ([number, number][] | null)
- Polygon coordinates are converted from page-normalized to
bounding-box-relative percentages for clip-path
All 687 existing frontend tests pass.
Refs #227
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
