zoom multiplies the baseline instead of being swallowed by it

The 2x cap flattened the panel's zoom control into doing nothing, and the
reason is worth writing down: `fit` is the SAME NUMBER at every zoom level.
CSS `zoom` takes off `offsetWidth` exactly what it adds to the pixel ratio, so
the fit is zoom-invariant by construction — and capping it therefore caps every
zoom level to the same size.

So the cap applies to the baseline, the size at 100%, and zoom multiplies what
comes out. 100% stays exactly where it is; zooming in goes past 2x again.

Quarter steps now go all the way down rather than whole numbers under 2x. With
whole numbers, zooming out from a 2x baseline fell straight to 1x and halved
the board in one press. Cells stay whole at every quarter — 20px at 1.25x —
which was always the property that mattered, not the size of the step.

The resulting ladder over the panel's 70-160% range: 1.25, 1.5, 1.75, 2.0,
2.0, 2.25, 2.5, 2.75, 3.0, 3.0. Eight of the ten presses move it; two land on
the same quarter, which is the price of keeping the grid even.

Also `overflow-hidden` on the box, so zooming past what the panel holds clips
rather than shoving the status line out of the way.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Officer-Session: de3ed4e6-f88a-429c-94e6-a760336ba83b

README.md

@@ -90,15 +90,20 @@ resizing the panel, and the surround is teal (`-solid`) rather than the root's b
 **The stage is small because the panel scales it by whole numbers.** Pixel art at a fractional scale gets
 uneven cells — some three screen pixels wide, their neighbours two — which reads as "not quite right"
 rather than as blur, and `image-rendering: pixelated` does not help because unevenness is not blur. So the
-panel snaps the scale, in DEVICE pixels, to whole numbers below 2x and QUARTER steps above it. Quarters are
-safe because the unit that has to stay regular is the CELL: the board is a 16px grid, so at 2.25x a cell is
-exactly 36 screen pixels, as even as at 2x, and only sub-cell pixels alternate. They are quarters rather
-than halves because coarse steps overshoot — with halves this jumped 2x to 2.5x, too small to too large
-with nothing in between.
+panel snaps the scale, in DEVICE pixels, to QUARTER steps. Quarters are safe because the unit that has to
+stay regular is the CELL: the board is a 16px grid, so every quarter step gives a whole cell — 20px at
+1.25x, 36px at 2.25x — and only sub-cell pixels alternate. Quarters rather than halves because coarse steps
+overshoot, and quarters all the way down rather than whole numbers under 2x because otherwise zooming out
+from a 2x baseline falls straight to 1x and halves the board in one press.
 
-The scale is then CAPPED at 2x. Fitting the panel is not the same as looking right, and past 2x this stops
-reading as a window on a desktop. That is a default, not a verdict — the panel header has a zoom control,
-and `MAX_SCALE` is one constant.
+The BASELINE — the size at 100% — is capped at 2x. Fitting the panel is not the same as looking right, and
+past 2x this stops reading as a window on a desktop.
+
+The panel's own zoom control then multiplies that, so zooming in still goes past 2x and zooming out still
+shrinks. This needs saying because it is not automatic: `fit` is the same number at every zoom level, since
+CSS `zoom` takes off `offsetWidth` exactly what it adds to the pixel ratio. A cap applied to the result
+rather than the baseline therefore flattens the zoom control into doing nothing, which is how the first
+version of it shipped.
 
 Two things the scale has to know about that are easy to miss. `devicePixelRatio` is not the whole story:
 the panel header has its own CSS `zoom`, so the effective ratio is `devicePixelRatio × zoom`, read as