feat(hero): stepped medallion relief, seated on the parapet face

The medallions were not just flat - they were buried. seat_on_front put
Hero_Medallion at offset 0.08 (front Y -0.42) while the 1.2 m-deep parapet stands
at Y -0.15, so both discs sat inside the parapet and never rendered. The motto
band and surround have the same burial (offset 0.06) and are a separate follow-up.

- Three stepped layers per medallion with per-layer prefixes so seat_on_front gives
  each its own stand-off: Rim (0.55 m, dark, offset 0.36 -> Y -0.14), Field
  (0.38 m, light, offset 0.43 -> Y -0.07), Boss (0.15 m, dark, offset 0.50 -> Y 0.00).
  A single Hero_Medallion prefix would both flatten the relief and (via startswith)
  swallow the specific prefixes, so it is removed.
- Moved from +/-6.2 (inside the inscription text, which spans +/-6.87) to +/-9.8.
- Fixed Tools/review/hero_iterate.sh, which still had the pre-tools-move
  'cd dirname/..' and landed in Tools/ instead of the repo root.

Rendered and judged; the advisory two-model judge (no, 0.93) no longer flags the
medallions. Owner review pending.

.gitignore

@@ -69,3 +69,5 @@ Thumbs.db
 
 # Unreal per-project build artefacts (FileOpenOrder logs and the like)
 Build/
+dsh-session-*
+tmp/