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>

utils/JWT/__init__.py

@@ -25,11 +25,11 @@ async def load_secret_key() -> None:
     从数据库读取 JWT 的密钥。
     """
     # 延迟导入以避免循环依赖
-    from sqlmodels.database import get_session
+    from sqlmodels.database_connection import DatabaseManager
     from sqlmodels.setting import Setting
 
     global SECRET_KEY
-    async for session in get_session():
+    async for session in DatabaseManager.get_session():
         setting: Setting = await Setting.get(
             session,
             (Setting.type == "auth") & (Setting.name == "secret_key")