Spinner tiles + flowing layout, per-section play, found vol/tone, reliable play

UX overhaul from feedback:

• Grid is no longer a rigid table. Each section is a block whose cells FLOW as self-labeled tiles (6 across on desktop, 3x2 on mobile) — fixes mobile width, no horizontal scroll.

• Every cell is a click-to-cycle SPINNER (right-click = back), incl. an "off" state. Dropdowns/popovers for options are gone

• Per-section ▶ (play just one section); ⚙ on synth tiles opens the synth editor.

• Found sound: per-source VOLUME + tone (lowpass) controls in the sources panel (instr 3 gains a cutoff p-field); role bed/solo dropped.

Verified: native render clean; headless shows 48 tiles, spinner cycles, ⚙ on 4 synth tiles, mobile reflows to 3 cols with no overflow.

▶ Play it: Rail Replacement Rapture — a bed-heavy genre where the found-sound layer carries the room https://stellate.app/?genre=transitwave&seed=7709&path=749.12536,768.12569,730.12569&xdur=13.122

a810361 https://github.com/aboard-io/stellate/commit/a8103615e2303988d17528ca558099e7959efba6