re(ui): size the rest() guess disc-wide, and refute my own proposed fix

Follows up the defect found last iteration: rest()'s dwell fallback is
guessing whenever it runs. Two things were open -- how big it is, and
whether "rest = the last keyframe" is the fix. Both are now answered, and
the second is answered no.

plateau_census.py walks the placement regions directly instead of going
through `screen info --geometry`, which decodes every texture and cannot
do a disc-wide pass in reasonable time. Its control reproduces GP_TITLE
build 7's three fallback elements and names ptlogo_eff3.t32 among them
before counting anything.

  elements with a keyframe group      15 493
  no plateau -> rest pose is guessed   3 807  (24.57 %)
    ... current rule returns invisible 1 711  (44.9 %)
    ... current rule returns scale=0     195  ( 5.1 %)
  the two candidate rules agree        1 911  (50.2 %)

195 elements get a rest pose with scale 0%, which is not a pose. And
disc-wide the choice of rule is not cosmetic: the candidates agree half
the time.

But the port's exposure is one element. Across main menu, EXTRAS, title
and the developer splash, 14 elements are plateau-less and the two rules
agree on 13. The single disagreement is palogo_anima_eff.t32.

And "last keyframe" loses there, on a control that needed no new capture:
the splash carries three sibling glows with identical structure and
identical times --

  palogo_gamearts_eff  15:a=0 30:a=255 45:a=255 -:a=0  plateau -> visible
  palogo_seta_eff      15:a=0 30:a=255 45:a=255 -:a=0  plateau -> visible
  palogo_anima_eff     15:a=0 30:a=255 45:a=212 -:a=0  no plateau

-- differing in one byte. "Last keyframe" makes anima alone invisible
while its two siblings stay lit. The capture agrees weakly: box-mean
ratios capture/render are gamearts 0.717, seta 0.723, anima 0.772, and a
glow we drew that the game does not would put anima below its siblings,
not above.

So the defect is measured and the fix is still undecided. Nothing in the
decoder changed.

docs/port/HANDOFF.md

@@ -282,8 +282,21 @@ authored version can be deleted.
   pose k **to** pose k+1; neither is held unless they are equal — which is a
   plateau, and the plateau path has already returned by then. **So any element
   with no two adjacent identical poses has a guessed rest pose**, in our renderer
-  and in anything built from it. You can test for that in one pass over the
-  keyframes; consider flagging it rather than inheriting our guess.
+  and in anything built from it. Measured disc-wide: **3 807 of 15 493 elements
+  (24.57 %)**, of which **195 get a degenerate `scale = 0 %` pose**, and the two
+  candidate rules agree only **50.2 %** of the time.
+  ✅ **This does not block you.** On the five screens the port needs, 14 elements
+  are affected and the candidate rules **agree on 13**. The single disagreement
+  is `palogo_anima_eff.t32` on the developer splash, and the current answer is
+  the defensible one there — see below. Still worth flagging plateau-less
+  elements in an export rather than silently inheriting our guess; it is one pass
+  over the keyframes.
+  🔴 **"rest = last keyframe" is refuted** as the fix. The splash has three
+  sibling glows with identical structure and times, differing in one byte
+  (`a=212` vs `a=255` at `t=45`); that rule would make `anima_eff` alone
+  invisible while its two siblings stay lit. The capture agrees weakly — box-mean
+  ratios capture/render are gamearts 0.717, seta 0.723, **anima 0.772**, and a
+  glow we drew that the game does not would put anima *below* its siblings.
   [`structures/ui-resting-pose.md`](../re/structures/ui-resting-pose.md)
   🟡 **The shift is still not adopted**, now for a different reason: it flips
   this element to the visibly wrong answer, so it and a decision about