[Test] (Retrace): make a retrace under MOBILEGL_PIPE_VERIFY prove it armed, and give the lane a label

- A retrace that exports MOBILEGL_PIPE_VERIFY=1 at a library configured without
  -DMOBILEGL_PIPE_VERIFY=ON is a no-op: the frames still match their goldens and the
  case reports green having compared nothing. run_trace_case.cmake now demands the
  evidence whenever the variable is set to anything but 0/false - mobilegl.log must
  exist, must carry "MGPipe: verify armed", and must carry neither
  Fatal{PipeVerifyDiffer nor Fatal{UnmigratedPipeInput. With the variable unset the
  script is byte-for-byte the old one.
- The Fatal scan is not redundant with the replay's exit status:
  MOBILEGL_PIPE_VERIFY_FATAL=0 is the supported triage configuration, and there a
  divergence is logged and counted rather than aborted, so the run would finish 0
  with its own report sitting unread in the log.
- LABELS retrace on both registrations: the lane was selectable only by regex, so
  `ctest -L retrace --no-tests=error` - the spelling that reds a lane which
  registered nothing - could not be written at all.
- "verify": true on eight cases (the five 180s cases plus minecraft-1.21.4-in-world,
  minecraft-1.21.4-fabric-sodium-in-world and improved-transparency-minecraft-26.3),
  and --format github-verify-matrix over that subset: 16 entries, against the full
  lane's 77. The verify build compares at every verb boundary and again at every
  accessor read, which the design budgets at 5-10x, so the per-push job runs the
  subset and the full sweep is a phase-exit / workflow_dispatch run.
- The flag is validated in the manifest loader, not at the matrix, so a non-boolean
  or a verify case excluded from CI is a loud error in every consumer instead of a
  subset that is quietly one case short.

tools/trace_replay/trace_cases.json

@@ -13,6 +13,7 @@
   "cases": [
     {
       "name": "OpenRA",
+      "verify": true,
       "trace_archive": "openra.tgz",
       "trace_file": "openra.trace",
       "golden": "openra.0000031249.png",
@@ -27,6 +28,7 @@
     },
     {
       "name": "minecraft-1.21.4-startup",
+      "verify": true,
       "trace_archive": "minecraft-1.21.4-startup.tgz",
       "golden": "minecraft-1.21.4-startup.0000092195.png",
       "target_call": 92195,
@@ -34,6 +36,7 @@
     },
     {
       "name": "minecraft-1.21.4-main-menu",
+      "verify": true,
       "trace_archive": "minecraft-1.21.4-main-menu.tgz",
       "golden": "minecraft-1.21.4-main-menu.0000481787.png",
       "alternate_golden": "minecraft-1.21.4-main-menu.0000481787-mali.png",
@@ -42,6 +45,7 @@
     },
     {
       "name": "minecraft-1.21.11-main-menu",
+      "verify": true,
       "trace_archive": "minecraft-1.21.11-main-menu.tgz",
       "golden": "minecraft-1.21.11-main-menu.0000205347.png",
       "target_call": 205347,
@@ -49,6 +53,7 @@
     },
     {
       "name": "minecraft-1.17-main-menu-854",
+      "verify": true,
       "trace_archive": "minecraft-1.17-main-menu-854.tgz",
       "golden": "minecraft-1.17-main-menu-854.0000117757.png",
       "target_call": 117757,
@@ -56,6 +61,7 @@
     },
     {
       "name": "minecraft-1.21.4-in-world",
+      "verify": true,
       "trace_archive": "minecraft-1.21.4-in-world.tgz",
       "golden": "minecraft-1.21.4-in-world.0000280000.png",
       "target_call": 280000
@@ -70,6 +76,7 @@
     },
     {
       "name": "minecraft-1.21.4-fabric-sodium-in-world",
+      "verify": true,
       "trace_archive": "minecraft-1.21.4-fabric-sodium-in-world.tgz",
       "golden": "minecraft-1.21.4-fabric-sodium-in-world.0000923340.png",
       "target_call": 923340,
@@ -277,6 +284,7 @@
     },
     {
       "name": "improved-transparency-minecraft-26.3",
+      "verify": true,
       "trace_archive": "improved-transparency-minecraft-26.3.tgz",
       "golden": "improved-transparency-minecraft-26.3.0002667619.png",
       "target_call": 2667619,