Fix cross-screen state isolation and element restoration

[veillette]

Summary

• scope keyboard shortcuts and undo history to the visible screen
• filter track snapping to the active screen’s registered tracks
• synchronize PhET-iO element replacement with scene lookup, trace invalidation, and view reconstruction
• advance generated IDs beyond restored sparse IDs and reject duplicate IDs
• add regression coverage for all four findings

Testing

• npm test — 421 tests passed
• npm run check — passed
• npm run lint — passed
• npm run build — passed, including PWA generation
• manually verified one-step undo and keyboard/grid isolation across Lab and Intro

Walkthrough

screen_isolation_and_single_step_undo.mp4

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[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None