Fixes the critical finding — Browse/curve-popup no longer trigger 60 Hz
whole-client repaints when the meter is invisible. Pushes the fast-path and
self-containment geometry into master_meter with tests; batches the four minor
findings.
hasLoop becomes user-owned with the gestures as shortcuts onto it; no format change. START uses overlay/trace, not accent/primary, which is the waveform's own fill.
Payload v12 appends the new velocity->pitch curve and folds the retired filter velAmount into its now-bipolar curve, so pre-v12 projects reopen sounding identical. Preview button takes a drawn play triangle.
daniel