feat(editor): clarify tempo map guidance

[ChrisBeWithYou]

Summary

• update the Tempo Map HUD to advertise right-click sync-point BPM/signature editing
• use compact HUD copy on narrower canvases
• update the Tempo Map button tooltip to match the current editing surface
• add focused HUD-copy helper coverage

Testing

• node --check screen.js
• node tests/tempo_map_guidance.test.js
• node tests/tempo_map_bpm.test.js
• node tests/tempo_map_timesig.test.js
• node tests/measure_readout.test.js

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/editor-tempo-map-guidance

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