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>

pyproject.toml

@@ -12,6 +12,7 @@ dependencies = [
     "asyncpg>=0.31.0",
     "cachetools>=6.2.4",
     "captcha>=0.7.1",
+    "cryptography>=46.0.3",
     "fastapi[standard]>=0.122.0",
     "httpx>=0.27.0",
     "itsdangerous>=2.2.0",
@@ -28,8 +29,16 @@ dependencies = [
     "redis[hiredis]>=7.1.0",
     "sqlalchemy>=2.0.44",
     "sqlmodel>=0.0.27",
+    "sqlmodel-ext[pgvector]>=0.1.1",
     "uvicorn>=0.38.0",
     "webauthn>=2.7.0",
+    "whatthepatch>=1.0.6",
+]
+
+[project.optional-dependencies]
+build = [
+    "cython>=3.0.11",
+    "setuptools>=75.0.0",
 ]
 
 [tool.pytest.ini_options]