818874e65c
Add global crop_fill percent (default 90, 1-100) as a settings key with FastAPI 4xx validation. Wires the value through to the inventory PNG encode (non-retro: stored PNGs untouched). Adds a throwaway TapePrototype.svelte behind ?tape-prototype for the #99 design sandbox. Gates: check_requirements PASS, check_coverage PASS, settings tests 8/8.