Add mesh isolation (Union-Find) with DICOM preview overlay

Created by: avinainder

Summary

• Isolate button: Union-Find connected-component analysis on the STL mesh keeps only the largest component (aorta + coronary tree), removing disconnected fragments (ribs, spine, noise). Supports undo to restore original mesh.
• Preview overlay fix: Fixed a race condition in the DICOM annotator where the isolation preview (green=coronary, blue=removed) was being overwritten by the plain DICOM image. Replaced async monkey-patching with Promise.all() so both images load in parallel before a single render call.
• CLAUDE.md: Adds worktree-local project instructions covering the critical RAS coordinate transform, do-not-modify files, and deployment notes.
• Gitignore: Adds .vercel and .playwright-mcp/ exclusions.

Test plan

• Load an STL in the viewer → click Isolate → confirm disconnected fragments removed, main tree remains
• Click ↩️ Undo → original mesh restored
• Open annotator at http://localhost:5050/annotator/ → click 👁️ Preview → green coronary overlay visible on DICOM slice, no race condition flicker
• Toggle Preview off → plain DICOM renders correctly

🤖 Generated with Claude Code