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>

ee/service/license_service.py

@@ -0,0 +1,49 @@
+"""
+许可证加载与缓存服务（编译为 .so）
+
+从环境变量 LICENSE_KEY 或 license.key 文件加载许可证，
+调用 verify_license() 验证后缓存结果。
+"""
+import os
+from pathlib import Path
+
+import aiofiles
+
+from ee.license import LicenseError, verify_license
+from ee.service import LicensePayload
+
+_cached_payload: LicensePayload | None = None
+
+
+async def load_and_validate_license() -> LicensePayload:
+    """
+    加载并验证许可证，成功后缓存。
+
+    加载优先级：
+    1. 环境变量 ``LICENSE_KEY``
+    2. 项目根目录 ``license.key`` 文件
+
+    :returns: 验证通过的 LicensePayload
+    :raises LicenseError: 未找到许可证 / 验证失败 / 已过期
+    """
+    global _cached_payload
+
+    raw: str | None = os.getenv("LICENSE_KEY")
+
+    if not raw:
+        key_path = Path("license.key")
+        if key_path.is_file():
+            async with aiofiles.open(key_path, 'r') as f:
+                raw = (await f.read()).strip()
+
+    if not raw:
+        raise LicenseError("未找到许可证：请设置 LICENSE_KEY 环境变量或提供 license.key 文件")
+
+    data = verify_license(raw)
+    _cached_payload = LicensePayload.model_validate(data)
+    return _cached_payload
+
+
+def get_cached_license() -> LicensePayload | None:
+    """获取已缓存的许可证载荷（未加载时返回 None）。"""
+    return _cached_payload