feat: add theme preset system with admin CRUD, public listing, and user theme settings

- Add ChromaticColor (17 Tailwind colors) and NeutralColor (5 grays) enums
- Add ThemePreset table with flat color columns and unique name constraint
- Add admin theme endpoints (CRUD + set default) at /api/v1/admin/theme
- Add public theme listing at /api/v1/site/themes
- Add user theme settings (PATCH /theme) with color snapshot on User model
- User.color_* columns store per-user overrides; fallback to default preset then builtin
- Initialize default theme preset in migration
- Remove legacy defaultTheme/themes settings

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

service/storage/__init__.py

@@ -18,3 +18,11 @@ from .exceptions import (
 )
 from .local_storage import LocalStorageService
 from .naming_rule import NamingContext, NamingRuleParser
+from .object import (
+    adjust_user_storage,
+    copy_object_recursive,
+    delete_object_recursive,
+    permanently_delete_objects,
+    restore_objects,
+    soft_delete_objects,
+)