Fixes the sole Round-3 wart: annotating one object from two views now yields
ONE anchor (the single-view fallback is superseded in place by the
triangulation, same id) instead of a sibling pair. Adds DELETE /api/anchors/{id}
(unlinks annotations, 404 on unknown) + a deletable anchor list in the
correction panel. db gains get/update/delete_anchor + get_annotations(event_id).
CR-3 filed (additive). Suite 101 -> 103; frontend build clean; delete UI
verified live (state + DOM + 3D scene stay consistent).
Also: docs/ideas.md (future extensions), plan/ISSUES.md (seeded with the
gemini-2.5-flash retirement, FIXED), plan/status/phase4.md.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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