WIP checkpoint: Group + membership models + migration

backend/alembic/versions/0001_initial.py

@@ -19,16 +19,16 @@ depends_on: Union[str, Sequence[str], None] = None
 
 def upgrade() -> None:
     """Upgrade database schema."""
-    # Create ENUM types
-    world_visibility = postgresql.ENUM(
+    # Create ENUM types (create once, reuse below)
+    world_visibility_enum = postgresql.ENUM(
         "public", "private", "friends_only", name="world_visibility"
     )
-    world_visibility.create(op.get_bind(), checkfirst=True)
+    world_visibility_enum.create(op.get_bind(), checkfirst=True)
 
-    asset_type = postgresql.ENUM(
+    asset_type_enum = postgresql.ENUM(
         "image", "audio", "video", "document", "model_3d", "other", name="asset_type"
     )
-    asset_type.create(op.get_bind(), checkfirst=True)
+    asset_type_enum.create(op.get_bind(), checkfirst=True)
 
     # Create users table
     op.create_table(
@@ -59,7 +59,7 @@ def upgrade() -> None:
     )
     op.create_index(op.f("ix_sessions_token"), "sessions", ["token"], unique=True)
 
-    # Create worlds table
+    # Create worlds table — reuse world_visibility_enum (no second create)
     op.create_table(
         "worlds",
         sa.Column("id", sa.Integer(), primary_key=True),
@@ -68,9 +68,7 @@ def upgrade() -> None:
         sa.Column("owner_id", sa.Integer(), nullable=False),
         sa.Column(
             "visibility",
-            postgresql.ENUM(
-                "public", "private", "friends_only", name="world_visibility"
-            ),
+            world_visibility_enum,
             nullable=True,
         ),
         sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now()),
@@ -79,7 +77,7 @@ def upgrade() -> None:
     )
     op.create_index(op.f("ix_worlds_id"), "worlds", ["id"], unique=False)
 
-    # Create assets table
+    # Create assets table — reuse asset_type_enum (no second create)
     op.create_table(
         "assets",
         sa.Column("id", sa.Integer(), primary_key=True),
@@ -87,10 +85,7 @@ def upgrade() -> None:
         sa.Column("description", sa.Text(), nullable=True),
         sa.Column(
             "asset_type",
-            postgresql.ENUM(
-                "image", "audio", "video", "document", "model_3d", "other",
-                name="asset_type",
-            ),
+            asset_type_enum,
             nullable=False,
         ),
         sa.Column("file_path", sa.String(length=512), nullable=False),