test: add unit tests for PhraseMakerGrid widget

[kh-ub-ayb]

Summary

This pr adds a new unit test suite for the PhraseMakerGrid widget module, covering all 8 of its grid/matrix state management methods with 61 comprehensive tests.

Changes

• Added 61 new unit tests in js/widgets/__tests__/PhraseMakerGrid.test.js
• No changes to source code

Test Coverage

Describe Block	Tests	Coverage
Module Export	8	Verifies all 8 method exports
clearBlocks	6	Resets _rowBlocks, _colBlocks, _rowMap, _rowOffset; preserves other properties
addRowBlock	6	Sequential adds, _rowMap / _rowOffset tracking, duplicate handling with 1000000 offset
addColBlock	5	Single/multi-entry adds, repeated rhythm blocks with index increment, n=0 edge case
addNode	7	_blockMap creation, node structure [row, [rhythm, n], j], duplicate j increment, separate blk keys
removeNode	6	Matching removal, non-matching preservation (different row/rhythm/n), blockNo-scoped mutation
mapNotesBlocks	7	Block chain traversal, name filtering, withName pairs, "all" mode excluding hidden/vspace/hiddennoFlow
lookForNoteBlocksOrRepeat	9	newnote / repeat flag detection, skip -1/null/undefined blocks, early exit, reset behavior
syncMarkedBlocks	6	-1 filtering, helper mapping, deduplication, empty/no-match edge cases, blockNo scoping

Scope

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

Verification

• All 61 tests pass

[github-actions]

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

[kh-ub-ayb]

@walterbender @omsuneri please review