v1.10.0

Additive (MINOR) release: a song-level harmony track. Backward-compatible — a 1.0.0 pack is also a
valid 1.10.0 pack, and older readers ignore the new optional manifest key + side-file.

Added

• Song-level harmony track — harmony.json (spec §7.8,
  manifest harmony key): the song's intended chord progression (the chords the song is,
  independent of what any arrangement plays) — reference/teaching data for fretboard-theory
  overlays, chord lyric lines, and practice-alongs. Time-ordered events applying until the next
  (same shape as keys.json): t (required), root (absolute note name; null marks a
  no-chord/N.C. event), quality, rn (Roman numeral relative to the active keys.json key,
  omitted when no key is active), and bass (slash-chord bass). Voicing-free (does not index
  arrangement chord templates) and honesty-ruled — a grader MUST NOT score against it. Defined
  as distinct from per-chord fn (as-played function): a Reader MAY derive one from the other, but
  neither is authoritative. quality/fn.q now reference a shared (recommended, not closed)
  chord-quality vocabulary so they stay interoperable. Schema:
  schemas/harmony.schema.json; exercised by the extended example
  (an Em→C→G→D7/F#→N.C. progression aligned to its Em/G keys.json). Implements #28.