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/routers/__init__.py

@@ -0,0 +1,6 @@
+from fastapi import APIRouter
+
+from .pro import router as pro_router
+
+ee_router = APIRouter()
+ee_router.include_router(pro_router)

ee/routers/pro/__init__.py

@@ -0,0 +1,69 @@
+"""
+Pro 版本状态端点
+
+提供许可证状态查询，需管理员权限。
+"""
+from datetime import datetime
+
+from fastapi import APIRouter, Depends
+
+from ee.service import LicensePayload
+from ee.service.license_service import get_cached_license
+from middleware.auth import admin_required
+from sqlmodel_ext import SQLModelBase
+
+router = APIRouter(prefix="/pro")
+
+
+class ProStatusResponse(SQLModelBase):
+    """Pro 版本状态响应"""
+
+    is_active: bool
+    """许可证是否有效"""
+
+    domain: str
+    """授权域名"""
+
+    expires_at: datetime
+    """过期时间"""
+
+    max_users: int
+    """最大用户数（0 = 无限制）"""
+
+    features: list[str]
+    """已授权的功能列表"""
+
+
+@router.get(
+    '/status',
+    dependencies=[Depends(admin_required)],
+)
+async def get_pro_status() -> ProStatusResponse:
+    """
+    查询 Pro 版本许可证状态
+
+    认证：
+    - JWT token in Authorization header
+    - 需要管理员权限
+
+    响应：
+    - ProStatusResponse: 当前许可证信息
+
+    错误处理：
+    - HTTPException 401: 未授权
+    - HTTPException 403: 非管理员
+    - HTTPException 500: 许可证缓存异常
+    """
+    payload: LicensePayload | None = get_cached_license()
+    if not payload:
+        # init_ee 成功后 payload 一定存在，此处做防御性编程
+        from utils.http.http_exceptions import raise_internal_error
+        raise_internal_error()
+
+    return ProStatusResponse(
+        is_active=True,
+        domain=payload.domain,
+        expires_at=payload.expires_at,
+        max_users=payload.max_users,
+        features=payload.features,
+    )