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/wopi/__init__.py

@@ -0,0 +1,11 @@
+"""
+WOPI（Web Application Open Platform Interface）路由
+
+挂载在根级别 /wopi（非 /api/v1 下），因为 WOPI 客户端要求标准路径。
+"""
+from fastapi import APIRouter
+
+from .files import wopi_files_router
+
+wopi_router = APIRouter(prefix="/wopi", tags=["wopi"])
+wopi_router.include_router(wopi_files_router)