feat(editor): expand snap grid options

[ChrisBeWithYou]

Summary

• expand editor snap options beyond 1/16 through 1/96
• include triplet-friendly snap divisions such as 1/12, 1/24, and 1/48
• make snap options data-driven while preserving the existing snap index model and 1/4 default
• add snap option model tests for labels and beat subdivisions

Testing

• node --check screen.js
• node tests/snap_options.test.js
• all tests/*.test.js via node

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/editor-expanded-snap-grid

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[byrongamatos]

Review pass (Claude Code) — stacked on #56. Own logic is correct: SNAP_OPTIONS (label/value/subdivisions) with SNAP_VALUES derived from it keeps the index model + 1/4 default (snapIdx: 2), _editorSnapSubdivisionsPure handles the 1/N→subdivisions math, and snapTime's if (!sv …) correctly treats the Off entry as no-snap. node --check + all JS tests green (3 snap-option tests).

⚠️ Conflict flag (not a bug here): this overlaps #46 (editor-snap-navigation), which also expands the snap grid but with an incompatible model — #46 removes SNAP_VALUES and adds a separate snapEnabled flag + triplet labels (1/3T, 1/12T), while this PR keeps SNAP_VALUES (derived) with an Off entry and plain 1/12/1/24 labels. Both redefine the same constants, so they can't both merge. Same family as the #46↔#55 nav conflict — worth deciding which snap model wins alongside items 2/3. (Codex rate-limited — manual + test-backed.)