tools: classify the mission briefing instead of filing it as menu

The briefing map is cyan and satisfies every clause of the menu rule (b-r > 30,
r < 45, little white), with no earlier rule claiming it -- so it was labelled
`menu`.  That made wait_screen.sh report NEVER REACHED READY ROOM on a run that
had successfully done LOAD GAME -> slot 01 -> YES and was three screens further
on: a working route scored as a failed one, pointing the next debugging step at
an input path that was fine.

Cyan has b and g nearly equal (b-g ~ 5) where the menu's blue leads its green
(b-g ~ 32), so `r < 20 and g > 30 and b - g < 20` separates them; the r floor
keeps the title screen out.  The file's own docstring already carried the
briefing's mean as an aside -- it just never had a class.

Verified against all eight signatures the file documents (2 menu variants, title,
ready room, flight, 3 briefing measurements): no regressions, and the captured
briefing image now reads `briefing`.

tools/re-capture/screen_id.py

@@ -23,7 +23,7 @@ Measured on known-good captures of each screen (1280x720, no menu bar):
     movie      green 0%     white varies                     no green at all
 
 Usage: screen_id.py <png> [--json]
-Prints one of: title | menu | readyroom | flight | other, plus the features.
+Prints one of: title | menu | briefing | readyroom | flight | other, plus the features.
 """
 import json
 import subprocess
@@ -73,6 +73,24 @@ def classify(f):
     # which put one run in OPTIONS and the next in BRIEFINGS.
     if f["b"] > 110 and f["r"] < 40 and f["b"] - f["g"] > 60:
         return "readyroom"
+    # The mission BRIEFING map is cyan, not blue, and without this rule it falls
+    # straight through to the menu test below (dark, b - r > 30, r < 45, little
+    # white -- all true of it). MEASURED 2026-08-26: that mislabel made
+    # `wait_screen.sh readyroom` report NEVER REACHED READY ROOM on a run that
+    # had in fact navigated LOAD GAME -> slot 01 -> YES and was sitting on the
+    # briefing three screens further on, which is the worst kind of failure --
+    # a successful route scored as a failed one.
+    #
+    # What separates them is that cyan has blue and green nearly equal, while
+    # the menu's blue runs far ahead of its green:
+    #
+    #   briefing   (1.4, 45.2, 49.6) (5.5, 49.1, 54.3) (4.6, 47.7, 54.5)  b-g ~ 5
+    #   main menu  (25, 38, 70)      (13, 26, 59)                         b-g ~ 32
+    #
+    # The r < 20 floor keeps the title screen (52.8, 66.1, 74.5, b-g 8.4) out;
+    # the ready room (b-g ~ 97) and flight (green rule) are already claimed above.
+    if f["r"] < 20 and f["g"] > 30 and f["b"] - f["g"] < 20:
+        return "briefing"
     # The main menu is dark and strongly blue. TWO measured signatures, not one:
     #
     #   white 3.5%   mean (25, 38, 70)   the 2026-07 reference at the top