1. drawOverlay: checkerboard mask overlay now drawn in axis + measure
states (mask carry-forward — slab is isolated)
2. Removed the separate red axis line + arrowhead — the rect's long
side IS the axis
3. Rect rotates: uses axisState.rect.angle (from UAT-8a)
4. Replace three rotate buttons with slider (-180..180, step 1) +
minus/plus nudge buttons (same pattern as Sensitivity slider)
587 lines, 109/109 tests, build OK.
Ty
2bc7eecd7c