权限管理：新增医学审核项目角色

新增 MEDICAL_REVIEW 项目角色，界面显示为医学审核，并通过 Alembic 迁移扩展 user_role 枚举。

为医学审核配置独立默认权限：项目总览、参与者、风险问题、监查稽查、FAQ、共享库按医学审核职责开放，不再复制 PV 默认权限。

同步前后端类型、项目成员角色下拉、权限矩阵展示、文件分发角色兜底和用户协议文案，并补充权限矩阵回归测试。

backend/app/core/project_permissions.py

@@ -7,7 +7,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.models.study_role_permission import StudyRolePermission
 
-PROJECT_PERMISSION_ROLES = ("ADMIN", "PM", "CRA", "PV", "IMP", "QA")
+PROJECT_PERMISSION_ROLES = ("ADMIN", "PM", "CRA", "PV", "MEDICAL_REVIEW", "IMP", "QA")
 
 PROJECT_PERMISSION_MODULES = (
     {"key": "project_members", "label": "项目成员", "description": "维护项目账号、成员角色与启停状态"},
@@ -93,6 +93,24 @@ DEFAULT_PROJECT_ROLE_PERMISSIONS: dict[str, dict[str, dict[str, bool]]] = {
         "sites": {"read": False, "write": False},
         "audit_export": {"read": False, "write": False},
     },
+    "MEDICAL_REVIEW": {
+        "project_overview": {"read": True, "write": False},
+        "project_milestones": {"read": False, "write": False},
+        "fees": {"read": False, "write": False},
+        "materials": {"read": False, "write": False},
+        "file_versions": {"read": False, "write": False},
+        "startup_ethics": {"read": False, "write": False},
+        "startup_auth": {"read": False, "write": False},
+        "subjects": {"read": True, "write": False},
+        "risk_issues": {"read": True, "write": True},
+        "monitoring_audit": {"read": True, "write": False},
+        "etmf": {"read": False, "write": False},
+        "faq": {"read": True, "write": True},
+        "shared_library": {"read": True, "write": True},
+        "project_members": {"read": False, "write": False},
+        "sites": {"read": False, "write": False},
+        "audit_export": {"read": False, "write": False},
+    },
     "IMP": {
         "project_overview": {"read": True, "write": False},
         "project_milestones": {"read": True, "write": False},