Add two OPTIONAL per-chord harmony annotations (feedpak 1.7.0), mirroring the
teaching-marks (fg/ch/sd) wire work:
- Chord.fn (instance): {rn, q, deg} harmonic-function object, key-dependent.
Validated by _validate_fn on BOTH decode and emit so a partial / out-of-range
fn (which would fail the schema's required-keys rule) never rides the wire.
Default-omitted, mirroring bend bnv.
- ChordTemplate.voicing (template): key-independent voicing-type string
("open", "triad", "shell", "drop2", "barre", ...). Emitted only when
non-empty; non-string wire values fall back to "".
Display/teaching only — never fed to a grader (honesty rule). fn auto-derivation
is DEFERRED (carry-only): a complete rn/q needs chord-quality analysis, and a
deg-only fn would be schema-invalid, so server.py carries author-provided fn
unchanged. GP import unchanged (no reliable per-chord function/voicing).
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
