Fix double CREATE TYPE crashes + oversized revision id in moderation migration

0001_initial.py: restore create_type=False on the two inline ENUM column
declarations (world_visibility, asset_type) -- this task's own auto-checkpoint
had accidentally reverted the 2026-08-18 fix (PR #25) while working on an
unrelated file.

0003_add_moderation_tables_and_user_roles.py: same bug pattern, self-inflicted
this time -- added create_type=False to all 8 inline column ENUM declarations
(user_role, target_type x2, reason_category, report_status, resolution,
action_type, appeal_status). Also shortened the revision id from
0003_add_moderation_tables_and_user_roles (42 chars) to 0003_moderation_schema
(23 chars) -- alembic_version.version_num is VARCHAR(32) by default, so the
migration ran to completion and then failed writing its own bookkeeping row.

Verified against a genuinely fresh Postgres container: full chain
(0001 -> 0002 -> 0003) now runs clean, all 8 tables land.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/alembic/versions/0001_initial.py

@@ -69,7 +69,8 @@ def upgrade() -> None:
         sa.Column(
             "visibility",
             postgresql.ENUM(
-                "public", "private", "friends_only", name="world_visibility"
+                "public", "private", "friends_only", name="world_visibility",
+                create_type=False,
             ),
             nullable=True,
         ),
@@ -89,7 +90,7 @@ def upgrade() -> None:
             "asset_type",
             postgresql.ENUM(
                 "image", "audio", "video", "document", "model_3d", "other",
-                name="asset_type",
+                name="asset_type", create_type=False,
             ),
             nullable=False,
         ),