re(ui): scale 0 means collapsed, not "unset" -- stop drawing it full size

blit() and fill_quad() both opened with

    let sx_pct = if kf.scale_x == 0 { 100 } else { kf.scale_x };

so an element whose pose is collapsed to nothing rendered at FULL SIZE.
I first described this as "a 1-pixel sliver", reading the .max(1) in the
size arithmetic two lines below -- the guard above it meant .max(1) never
saw a zero. Read the whole function, not the lines you went looking for.

Control run before the change: if 0 meant "unset", something on the disc
would use it throughout. Nothing does.

  elements with a keyframe group                    15 493
  at least one keyframe at scale 0                   2 166
  EVERY keyframe at scale 0                              0
  zero is a transient the element grows out of       1 762

ptlogo_eff3.t32 runs 0% -> 200%. An "unset" marker no element ever uses
throughout is not a marker.

Both functions now return without drawing when either scale is 0.

Reach: 24 of 24 renders byte-identical across GP_TITLE (all 16 builds),
GP_PAUSE_MENU and GP_OPTIONS -- additive on every screen the port needs.
195 elements have a guessed rest pose at scale 0 and 126 of those have a
non-zero alpha, so the old code painted them; all 126 are in
GP_READY_ROOM.pak, which S1 already declared a no-go. They are
tactical-map sprites at sx=0/sy=100, mid-horizontal-wipe, that the
coercion drew full-width.

So: a real correctness fix with no visible effect on the menu port.
Suite green, 122 passed / 0 failed across 3 suites at commit time.

docs/re/REFUTED.md

@@ -408,3 +408,8 @@ neighbourhood, not just the line.
   makes `palogo_anima_eff` alone invisible while `gamearts_eff` and `seta_eff`
   stay lit. Capture box-mean ratios (0.717 / 0.723 / **0.772**) go the other way
   too. [`structures/ui-resting-pose.md`](structures/ui-resting-pose.md)
+* "a keyframe `scale` of 0 means *unset*, so render at 100 %" → **refuted by a
+  disc-wide control.** 2 166 elements have a zero-scale keyframe and **not one is
+  zero on every keyframe**, while 1 762 grow back out of zero (`ptlogo_eff3.t32`
+  runs 0 % → 200 %). Zero means collapsed; the renderer now draws nothing.
+  [`structures/ui-rat-layout.md`](structures/ui-rat-layout.md)