canawave: U2-style 16th-note arp guitar (1/4T delay) + grand brass swell

engine: add `arp16` 16th-note arpeggio melody pattern

• canawave delay → quarter-note-triplet (0.667 beat) with cascading feedback; the guitar arp (kpluck, low drive, high delay send) chimes through it = U2/Edge

• guitar arp now runs the band sections (verse/chorus/verse2/chorus2)

• bridge is now a big grand triumphant brass swell at the midpoint (loud brass on the anthem theme, sweep open, tom fill) — the brass finally speaks

• structure/length unchanged, so the audio grafts onto the existing video

Verified: matrix 17/17; existing genres render unchanged.

▶ Play it: Loon Referendum — parked on the genre this change names https://stellate.app/?genre=canawave&seed=2986&path=1505.3698,1524.3731,1486.3731&xdur=13.122

9c74333 https://github.com/aboard-io/stellate/commit/9c74333adca719add85515fa2bd12a0cd77b314c