feat: generate bounded ascending and descending MIDI arpeggio patterns

docs/COMPOSITION_WORKFLOWS.md

@@ -34,3 +34,7 @@ Edit/MIDI tools/Humanize applies timing variation up to 960 ticks and velocity v
 ## Phase 65 — Chord Construction
 
 Edit/MIDI tools/Build chords accepts 1..8 unique nonzero semitone intervals, such as 4 7 for a major triad or 3 7 for minor. Originals remain; added notes copy timing, velocity and channel. Negative intervals support lower voicings. All source notes are processed, including hidden trimmed notes. Pitch overflow or capacity rejects the whole operation; existing unisons are not deduplicated.
+
+## Phase 66 — Offline Arpeggio Generation
+
+Edit/MIDI tools/Generate arpeggio replaces source notes with a written pattern. Equal-onset notes on the same channel form a chord lasting until its longest note end. The pattern cycles sorted pitches upward or downward, with the selected step and gate. Each step inherits its chosen note velocity/channel. All source notes, including hidden trimmed notes, participate. This is offline generation with undo, not a live arpeggiator or tempo-synced MIDI effect.