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>

tests/unit/models/test_setting.py

@@ -113,7 +113,7 @@ async def test_setting_update_value(db_session: AsyncSession):
     setting = await setting.save(db_session)
 
     # 更新值
-    from sqlmodels.base import SQLModelBase
+    from sqlmodel_ext import SQLModelBase
 
     class SettingUpdate(SQLModelBase):
         value: str | None = None