Add writeMidiFile() with TEMPO/EVENTS/unrecognized-track emission

[elicwhite]

Port of the core MIDI writer infrastructure:

• writeMidiFile(chart) entry point: builds a Format-1 MIDI and returns
  Uint8Array via midi-file's writeMidi
• TEMPO TRACK: trackName + setTempo (from chart.tempos) + timeSignature
  (from chart.timeSignatures), all at their absolute ticks
• EVENTS track: trackName + section text events (unwrapped so YARG's
  NormalizeTextEvent doesn't strip names containing ]) + [end] events +
  global events (bracket-wrap when source is .chart so MIDI output
  follows convention) + [coda] derived from drumFreestyleSections when
  not already present in unrecognizedEvents
• Unrecognized MIDI tracks: verbatim pass-through with abs-tick →
  delta-tick conversion; duplicate track names suffixed to keep the
  internal trackMap unique
• finalizeMidiTrack helper: sorts by tick with a type-priority
  tiebreaker, converts absolute ticks to delta times, appends endOfTrack

Instrument tracks (PART DRUMS, PART GUITAR, …) and vocal tracks
(PART VOCALS, HARM1/2/3) land in follow-up PRs.

[elicwhite]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Add ChartDocument + writeChartFolder orchestrator #78 : 2 dependent PRs (#79 , #87 )
• Add same-format round-trip integration tests #77
• writeMidiFile: emit PART VOCALS / HARM1 / HARM2 / HARM3 tracks #76
• writeMidiFile: emit PART GUITAR / GHL instrument tracks #75
• writeMidiFile: emit PART DRUMS instrument tracks #74
• Add writeMidiFile() with TEMPO/EVENTS/unrecognized-track emission #72 👈 (View in Graphite)
• writeChartFile: emit instrument track sections #71
• Add writeChartFile() with Song/SyncTrack/Events/unrecognized-section emission #70
• Add writeIniFile() for song.ini emission #69
• Add createEmptyChart() counterpart to parseChartAndIni #68
• Add shared File type in interfaces.ts #86
• master

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