feat(demo): full 31-command MIDI porcelain reference + docs (#121)

Expands the MIDI demo page and documentation to cover all 31 semantic porcelain commands introduced across the original 11 and the new 20.

midi-demo.html: - CLI reference section now organised into 8 named groups with header cards (icon · title · desc · command count) - Group 1 — Notation & Visualization (notes, piano-roll, instrumentation) - Group 2 — Pitch, Harmony & Scale (harmony, scale, contour, tension, cadence) - Group 3 — Rhythm & Dynamics (rhythm, tempo, density, velocity-profile) - Group 4 — Structure & Voice Leading (motif, voice-leading, compare) - Group 5 — History & Attribution (note-log, note-blame, hotspots) - Group 6 — Multi-Agent Intelligence (agent-map, find-phrase, shard, query) - Group 7 — Transformation (transpose, invert, retrograde, quantize, humanize, arpeggiate, normalize, mix) - Group 8 — Invariants & Quality Gates (check) - All 31 cards include live terminal examples with syntax-highlighted output - Added .cli-group-section/.cli-group-hd CSS; group count badges

docs/demo/demo-midi.md: - Added Acts X–XV covering all 20 new commands with full CLI output examples, usage snippets, and agent workflow notes - Full 31-command matrix table at the bottom, grouped by category - Updated "For AI Agents" section to reference all six capability dimensions

Co-authored-by: Gabriel Cardona <gabriel@tellurstori.com>