Summary

• Rectangle cutout drag-resize was floored at 10mm per dimension (radius 5mm for circle/square), an arbitrary default carried from the initial release with no geometric justification. The reporter wanted a 25x5mm slot.
• New floor is 1mm per dimension (0.5mm radius): the practical FDM printing floor. Backend verified safe down to 1x1mm: cutters are plain solids, fillet radii self-clamp, clearance buffers only apply to traced polygon outlines.
• Resize maths extracted from the component into pure helpers (resizeRectCutout, resizeRoundCutout) with unit tests, including a mutation-guard against the floor regressing.

Test evidence

• Frontend vitest: 90/90, 10 new tests (25x5mm allowed, sub-floor clamps, rotation-local dims, midpoint centring, radius floor regression guard). New tests verified red before the fix.
• Backend pytest: 235/235, 6 new tests: 1x1mm and 25x5mm cutters produce valid geometry with correct extents; full generate_bin for the reporter's exact 25x5mm case yields a valid STL that removes material.
• make lint: 0 errors.

Closes #114