formats: a third measured paint order — the main menu, with two primitives

Read off the running game with screen_children.py and identified by pivot
signature as GP_TITLE.pak ratc-index 8, the NEW GAME / LOAD GAME / TUTORIAL /
OPTIONS / EXTRAS screen:

  paint order: 1 3 4 2 5 8 9 6 7 15 10 11 12 13 14 0

It is the first measured screen carrying TWO primitives, and they land in
different places, which is the point. pteff02.prm (the 25% dim) paints 4th,
beneath the whole UI; pteff00.prm (the transition fade, resting transparent)
paints last. Both match their positions on the title screen exactly. So a
primitive's place is per-element and stable by role - backdrop first, dim at
slot 4, fade last - and there are now three permutations to test a derivation
against rather than two.

Wired into measured_paint_order, keyed by element names so both language builds
get it. The English build composited with --primitives edge-correlates at 0.9591
at shift (0,0) against a framebuffer capture taken in the same session - a third
screen confirming paint order, resting pose, fade alpha and primitives at once,
against a capture this project had not seen before.

13 disc tests green.

crates/sylpheed-formats/src/ui_layout.rs

@@ -728,6 +728,22 @@ fn measured_paint_order(build: &UiBuild) -> Option<Vec<usize>> {
         // the full-screen .prm, then all three glows, then the three logos.
         return Some(vec![0, 2, 4, 6, 1, 3, 5]);
     }
+    // GP_TITLE.pak ratc-index 8 — the MAIN MENU (NEW GAME / LOAD GAME /
+    // TUTORIAL / OPTIONS / EXTRAS). Read off the running game 2026-08-19; it is
+    // the third measured permutation and the first that contains TWO
+    // primitives, which is why it matters — see `ui-prm-primitives.md`.
+    const MENU: [&str; 16] = [
+        "pteff00.prm", "ptbase.t32", "pteff05.t32", "ptloop01.rat",
+        "ptloop02.rat", "pteff02.prm", "ptframe1.t32", "ptframe2.t32",
+        "pteff10.t32", "pteff12.t32", "ptbtn01.rat", "ptbtn02.rat",
+        "ptbtn03.rat", "ptbtn04.rat", "ptbtn05.rat", "ptmsg.t32",
+    ];
+    if names == MENU {
+        // background, the two loops, the full-screen effect, the DIM quad,
+        // the glows, the frames, the message, the five buttons, and the
+        // screen-transition FADE quad last.
+        return Some(vec![1, 3, 4, 2, 5, 8, 9, 6, 7, 15, 10, 11, 12, 13, 14, 0]);
+    }
     None
 }