test: add unit tests for PhraseMakerUI widget

[kh-ub-ayb]

Summary

This PR adds a new unit test suite for the PhraseMakerUI widget module, covering all 7 of its UI rendering and interaction methods with 49 comprehensive tests.

Changes

• Added 49 new unit tests in js/widgets/__tests__/PhraseMakerUI.test.js
• No changes to source code

Test Coverage

Describe Block	Tests	Coverage
Module Export	7	Verifies all 7 method exports
calculateNoteWidth	10	Eighth/quarter/half/whole/sixteenth notes, minimum width (15), _cellScale multiplier, floor rounding, fractional noteValue
highlightCell	5	Sets selectorBackground, missing row/cell guards, multi-cell targeting, multi-row targeting
unhighlightCell	5	Resets to rhythmcellcolor, skips non-highlighted cells, missing row/cell guards, scoped unhighlight
updateNoteCellVisual	7	Active sets background + checkmark, inactive clears both, null/undefined cell guards, toggle round-trip
updatePlayButton	8	Null/undefined _playButton guards, stop/play SVG sources, title text, ICONSIZE dimensions, toggle switching
resetMatrix	6	Resets noteValueRow cells, skips tuplet row when disabled, resets tuplet row when enabled, empty cells, different colors per row type

Scope

• Only js/widgets/__tests__/PhraseMakerUI.test.js was added
• No changes to source code

Verification

• All 49 tests pass

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[kh-ub-ayb]

@walterbender @omsuneri please review