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>

.dockerignore

@@ -0,0 +1,37 @@
+.git/
+.gitignore
+.github/
+.idea/
+.vscode/
+.venv/
+.env
+.env.*
+.run/
+.claude/
+
+__pycache__/
+*.py[cod]
+
+tests/
+htmlcov/
+.pytest_cache/
+.coverage
+coverage.xml
+
+*.db
+*.sqlite
+*.sqlite3
+*.log
+logs/
+data/
+
+Dockerfile
+.dockerignore
+
+# Cython 编译产物
+*.c
+build/
+
+# 许可证私钥和工具脚本
+license_private.pem
+scripts/