Move hasLyrics/hasVocals/hasForcedNotes from ParsedChart to ScannedChart (state-derived)

[elicwhite]

The three derived boolean flags on ParsedChart (hasLyrics, hasVocals,
hasForcedNotes) were parse-time snapshots that went stale whenever
consumers mutated chart data post-parse. Remove them from ParsedChart
entirely; scanChart derives all three at scan time from the current
chart state, piggybacking on its existing single note-walk (no extra
iterations).

• hasLyrics / hasVocals: computed from parsedChart.vocalTracks.parts —
  constant-time existence check.

• hasForcedNotes: inverts resolveFretModifiers. A note is 'forced' iff
  its resolved flag disagrees with the natural HOPO state the parser
  would pick without any force events, or it carries the tap flag
  (tap can only come from explicit forceTap). Inlined helpers for
  isNaturalHopo, isFretChord, isSameFretNote, isInFretNote,
  computeHopoThresholdTicks in chart-scanner.ts (duplicated from
  notes-parser.ts; a follow-up can extract to a shared helper).

Semantic change to note: under the new definition, redundantly-applied
force events (e.g. explicit forceHopo on a naturally-HOPO note) no
longer contribute to hasForcedNotes — the chart plays identically with
or without them, so state-derived detection correctly says false. This
eliminates the need for any 'hasForcedNotes backstop' in writers since
the flag round-trips naturally: the writer emits force events exactly
when a flag disagrees with natural state, and the scanner detects
those same disagreements on re-parse.

ScannedChart.notesData's shape is unchanged (hasLyrics / hasVocals /
hasForcedNotes still present); only the population source changes.

Consumers that previously read parsedChart.hasLyrics /
parsedChart.hasVocals / parsedChart.hasForcedNotes must switch to
scanChart output.

[elicwhite]

• perf: swap writer's spread-with-deltaTime for Object.assign #81
• perf: midi-file Writer uses preallocated Uint8Array #80
• perf: patch midi-file writeBytes to in-place push loop #79
• Add ChartDocument + writeChartFolder orchestrator #78
• 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
• 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
• Extract shared natural-HOPO helpers into natural-hopo.ts #73
• Move hasLyrics/hasVocals/hasForcedNotes from ParsedChart to ScannedChart (state-derived) #67 👈 (View in Graphite)
• Consolidate song metadata onto parsedChart.metadata #66
• master

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