refactor(kit): SM_ asset naming and topology validation per the modeling checklist

- Kit pieces export as SM_Kit_* (Unreal static-mesh convention) while the Blender
  objects keep their readable names; the kit loader strips the prefix so layout
  still addresses pieces by short name.
- facade_kit_build.py validates each piece before handoff (non-manifold edges,
  loose vertices, triangle count) and records the result in the part report:
  16 pieces, all manifold, no loose geometry, 12 tris each.
- ue_import_facade_kit.py removes kit assets the current build no longer produces,
  so a rename cannot leave two generations of the same piece behind.
- Kit re-imported and re-applied (625 pieces); packaged QA still PASS.

Tools/ue_import_facade_kit.py

@@ -42,6 +42,16 @@ def main() -> None:
         log(f"no FBX files in {SRC}")
         return
 
+    # Drop kit assets that the current build no longer produces (the pieces were
+    # renamed to follow the SM_ convention), so the folder cannot accumulate two
+    # generations of the same piece.
+    expected = {os.path.splitext(f)[0] for f in files}
+    for existing in unreal.EditorAssetLibrary.list_assets(DEST, recursive=False):
+        name = existing.split("/")[-1].split(".")[0]
+        if name not in expected:
+            unreal.EditorAssetLibrary.delete_asset(f"{DEST}/{name}")
+            log(f"removed stale kit asset {name}")
+
     for filename in files:
         asset_name = os.path.splitext(filename)[0]
         task = unreal.AssetImportTask()