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>

routers/api/v1/__init__.py

@@ -10,6 +10,7 @@ from .download import download_router
 from .file import router as file_router
 from .object import object_router
 from .share import share_router
+from .trash import trash_router
 from .site import site_router
 from .slave import slave_router
 from .user import user_router
@@ -29,6 +30,7 @@ if appmeta.mode == "master":
     router.include_router(object_router)
     router.include_router(share_router)
     router.include_router(site_router)
+    router.include_router(trash_router)
     router.include_router(user_router)
     router.include_router(vas_router)
     router.include_router(webdav_router)