docs: the splash .prm measured -- and its paint order is a sequence, not depth

ui-prm-primitives recorded that where a .prm paints on a screen without a
measured order is unsolved. For the developer splash it is now measured.

Every frame opens with two full-screen draws before any sprite. The
second is untextured in all 212 frames with a constant vertex colour of
FF000000 -- opaque black -- matching palogo_eff0.prm's declaration
exactly: kind 0x10, pivot (640,360) -> 1280x720, one keyframe, a = 255.
So the splash backdrop is an opaque black full-screen quad from the
bundle itself, painted behind every sprite, which is why a splash render
needs --black rather than the default backdrop.

Not a general rule, and said so: the measured main-menu order puts
pteff02.prm at position 4 and pteff00.prm LAST, the latter being the
screen-transition fade.

And a correction to an existing row. measured_paint_order returns
[0, 2, 4, 6, 1, 3, 5] for the splash, described as "the .prm, then all
three glows, then the three logos". But the glows and the logos never
appear in the same frame -- 0 overlapping frames in 235 -- and two
elements that never co-occur have no observable relative depth. Between
those halves the vector records the order they were SEEN IN, not a
front-to-back relationship.

That does not make the render wrong, and element 0 is a real depth
observation since the .prm co-occurs with everything. But the type of the
claim matters: reading the vector as depth invites compositing all seven
elements at once, which is exactly what does not reproduce the screen.

METHOD: two things that never co-occur have no observable relative order;
when recording an order, note which pairs actually appeared together.

docs/re/METHOD.md

@@ -826,3 +826,11 @@ agent's loop prompt, i.e. nowhere durable. See [`README.md`](README.md) for the
   four-entry enumeration showed none exists, and the question closed statically.
   A hypothesis that predicts an artefact can be killed by looking for the
   artefact, which is often far cheaper than measuring the behaviour.
+* **Two things that never co-occur have no observable relative order.** A
+  "measured paint order" recorded from a running game looks like depth
+  information throughout, but between elements that never share a frame it can
+  only be the sequence they were *seen in*. The splash's vector mixes both kinds
+  — element 0 is real depth (it co-occurs with everything), the glow/logo split
+  is not — and the difference matters, because reading it as depth invites
+  compositing every element at once. When recording an order, note which pairs
+  actually appeared together.