notepat: move m4l/os/drum into dedicated OS bar row
They were pinned to y=0 in the top bar and anchored to waveBtn, crowding
wave/oct and contesting hit areas with the mini-piano strip — which is
why they felt like they weren't linking. The OS_BAR slot (y=33–45) was
already reserved by the layout, just unused. Builders now position into
that row with responsive padding/labels; paint functions fill the box
directly instead of compensating for top-bar placement.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>