The UI runs on Arduino's loop task, whose stock 8 KB stack had 340 B left
at its deepest point; a screenshot's file write went past it and reset the
device. The loop stack is now 16 KB (measured peak ~7.8 KB) and the
screenshot's line buffer is static. Diagnostics names the row
"UI stack free (lowest)".
With a cable in at boot, the USB popup waited for nothing and showed over
the splash; it now comes once the splash has faded.
Adds docs/development/plan-next.md, the plan up to the merge into dev.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
