re(ui): the keyframe-time shift is favoured 26x by timing, rejected by a render

Follow-up on last iteration's unadopted candidate (+36 holds the NEXT
pose's time, not its own). Two new results, pointing opposite ways, and
both are reported.

FOR, and calibration-free: the observed full-alpha hold : fade-out ratio
on palogo_gamearts is 83 : 13 frames = 6.38. The shifted reading predicts
8.00. The current reading predicts 0.25 -- off by 26x. With the glow's 2
units/frame fixed and nothing else free, the current reading says the
logo holds full alpha for 2.0 frames; the capture holds it for 83. This
is no longer the shape argument the candidate rested on.

Also for: rest()'s plain max-dwell fallback picks a=0 -- a transparent
pose, for a publisher logo -- under the current reading, and the visible
a=255 hold under the shift. Only the rest_plateau special case rescues
the render today, and that is the case the port agent reported a bug in.

AGAINST: rendering every build of six UI paks under both readings, 10 of
11 compared are byte-identical and one changes -- GP_TITLE build 7, the
Japanese twin of build 4, by 13.1% of pixels. Build 4, the one verified
against a live capture, is unchanged either way, so the single build the
shift moves is the one with no capture to adjudicate it. The proxy goes
against the shift: language twins are the same artwork, and build 7 reads
70.94 mean luminance as decoded against build 4's 71.41, but 76.32
shifted. Correlation does not separate them (0.6206 vs 0.6201).

These constrain different things -- timing versus pose selection -- and
rest() is a heuristic layered on the times, so moving the times moves its
tie-breaks. Adopting the shift means revisiting that heuristic in the
same change, with no build-7 capture to verify against.

Default UNCHANGED. Experiment reachable via SYLPHEED_KF_TIME_SHIFT=1.
Shifted-mode suite: 122 passed, 0 failed across 3 suites at commit time.

docs/re/REFUTED.md

@@ -385,3 +385,9 @@ neighbourhood, not just the line.
   after its declared `a=32`, and its declared 80-frame fade-in is never drawn.
   The `_eff` glows do reproduce, exactly — so this is about the group timeline,
   not about the interpolation law. [`ui-keyframe-time-unit.md`](ui-keyframe-time-unit.md)
+* "the `_eff` elements' agreement is the whole case for the keyframe-time shift,
+  so it stays a shape argument" → superseded. The **hold duration** is
+  calibration-free and decides it: observed 83 frames of full alpha against a
+  predicted **2.0** as decoded and **80.0** shifted. The shift is nonetheless
+  **not adopted** — it moves `GP_TITLE` build 7 by 13 % of pixels, away from its
+  verified English twin's brightness. [`ui-keyframe-time-unit.md`](ui-keyframe-time-unit.md)