feat: migrate ORM base to sqlmodel-ext, add file viewers and WOPI integration

- Migrate SQLModel base classes, mixins, and database management to
  external sqlmodel-ext package; remove sqlmodels/base/, sqlmodels/mixin/,
  and sqlmodels/database.py
- Add file viewer/editor system with WOPI protocol support for
  collaborative editing (OnlyOffice, Collabora)
- Add enterprise edition license verification module (ee/)
- Add Dockerfile multi-stage build with Cython compilation support
- Add new dependencies: sqlmodel-ext, cryptography, whatthepatch

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

routers/api/v1/user/settings/__init__.py

@@ -17,12 +17,14 @@ from sqlmodels.color import ThemeColorsBase
 from sqlmodels.user_authn import UserAuthn
 from utils import JWT, Password, http_exceptions
 from utils.password.pwd import PasswordStatus, TwoFactorResponse, TwoFactorVerifyRequest
+from .file_viewers import file_viewers_router
 
 user_settings_router = APIRouter(
     prefix='/settings',
     tags=["user", "user_settings"],
     dependencies=[Depends(auth_required)],
 )
+user_settings_router.include_router(file_viewers_router)
 
 
 @user_settings_router.get(