v1.5.0

Additive (MINOR) release: per-note teaching marks. Backward-compatible — a 1.0.0 pack is also a
valid 1.5.0 pack, and older readers ignore the new optional note fields.

Added

• Per-note teaching marks (spec §6.2.2):
  three OPTIONAL note fields that annotate how a note is taught or displayed, never whether it was
  played correctly (the honesty rule — graders MUST NOT score them) — fg (fret-hand finger,
  -1 unset / 0 thumb / 1–4 index→pinky, same convention as template.fingers), ch
  (strum-group key: notes sharing a value ≥ 0 are one strum/rake gesture, with pkd giving
  direction), and sd (scale degree as a chromatic offset 0–11 above the active
  keys.json tonic; derivable, so a Reader MAY compute it).
  Schema: fg / ch / sd on $defs/note in
  schemas/arrangement.schema.json; exercised by the extended
  example pack (an Em-triad rake grouped by ch).