功能(提醒)：统一项目提醒中心与桌面通知链路

增加通用提醒状态、数据库迁移和定时同步，覆盖风险时效、文件回执、项目里程碑、访视窗口与协作申请。

新增网页端和桌面端提醒中心、真实投递诊断与固定隐私通知正文，并补齐登录来源聚合、测试和说明文档。

backend/app/api/v1/desktop_notifications.py

@@ -75,12 +75,12 @@ async def acknowledge_notifications(
     )
 
 
-@router.post("/{distribution_id}/read", status_code=status.HTTP_204_NO_CONTENT)
+@router.post("/{notification_id}/read", status_code=status.HTTP_204_NO_CONTENT)
 async def mark_notification_read(
-    distribution_id: uuid.UUID,
+    notification_id: uuid.UUID,
     db: AsyncSession = Depends(get_db_session),
     current_user=Depends(get_current_user),
 ) -> None:
     await desktop_notification_service.mark_notification_read(
-        db, current_user.id, distribution_id
+        db, current_user.id, notification_id
     )