`decimals` only reached `formatNumber`, so it changed the label and nothing else: typing 640.5 into
a field with `decimals: 0` stored 640.5 and displayed 641. The two existing users got away with it
because rounding happened outside the widget (`normalizeFrameRect`, the slice dialog), which their
comments had to point out.
`NumberField.clampValue` now rounds before it clamps, and every path that sets a value goes through
it (typing, scrubbing, arrow keys, the constructor), so the stored number matches the shown one and
`min`/`max` stay exact. The rounding is `roundTo` in math.ts, which `snapToStep` already did inline.
With that safe, camera `View width`/`View height` and text `Font size` become integers – they were
showing 640.000 and 32.000. Everything else that looked integral is not: positions, sprite and
collider sizes and zoom are all scrubbed, and `z` is a summed coordinate (walk.ts), not a layer.
Verified remotely against the RTX 4070 host: 270 checks, all passed (step 10 gained a check that the
field text has no decimal point and survives a reopen). `npm run check` green, 407 tests.