fix(photos): overlay UAT nits + 90% crop fill (#67,#68)

Length dim already mask tip-to-tip (locked by test). Width labels move
axis-left off the wood via labelAt; font steps down to max(22, scale*1.0).
Inventory/overlay crop FILL 0.8→0.9; CAPTURE/PHOTOS docs match.

frontend/src/png/inventory.ts

@@ -1,7 +1,7 @@
 import type { Mask, Source } from '../capture/capture.types';
 
 const FLOOR = 800; // shorter side, px
-const FILL = 0.8; // 80% fill at the widest and tallest points of the slab
+const FILL = 0.9; // 90% fill at the widest and tallest points of the slab
 const ASPECT_W = 3;
 const ASPECT_H = 4;