Add TownSquare scene assets, resource production docs, and model pipeline updates.

Bring in plaza props/prefabs, ZhaoYun source GLB, design originals, and Hunyuan/Blender tooling used to produce them.

Co-authored-by: Cursor <cursoragent@cursor.com>

Tools/hunyuan_3d/auth.py

@@ -81,7 +81,17 @@ def status() -> dict:
 
 
 def is_logged_in() -> bool:
-    return storage_state_path().is_file()
+    path = storage_state_path()
+    if not path.is_file() or path.stat().st_size < 8:
+        return False
+    try:
+        with path.open("rb") as fp:
+            if fp.read(1) != b"{":
+                return False
+        json.loads(path.read_text("utf-8"))
+        return True
+    except (OSError, ValueError, UnicodeDecodeError):
+        return False
 
 
 def logout() -> dict: