feat: add role/permission system with tests support

- Add Role model with 17 default permissions
- Add init_wizard to create admin/guest roles on first startup
- Protect admin role from modification/deletion via API
- Fix MilestoneCreate schema (project_id optional)
- Fix delete role to clean up role_permissions first
- Add check_project_role RBAC function

app/api/routers/roles.py

@@ -26,8 +26,8 @@ class PermissionResponse(BaseModel):
 class RoleResponse(BaseModel):
     id: int
     name: str
-    description: str | None
-    is_global: bool
+    description: str | None = None
+    is_global: bool | None = None
     permission_ids: List[int] = []
     
     class Config:
@@ -37,8 +37,8 @@ class RoleResponse(BaseModel):
 class RoleDetailResponse(BaseModel):
     id: int
     name: str
-    description: str | None
-    is_global: bool
+    description: str | None = None
+    is_global: bool | None = None
     permissions: List[PermissionResponse] = []
     
     class Config:
@@ -141,6 +141,10 @@ def update_role(role_id: int, role: RoleUpdate, db: Session = Depends(get_db), c
     if not db_role:
         raise HTTPException(status_code=404, detail="Role not found")
     
+    # Prevent modifying the admin role
+    if db_role.name == "admin":
+        raise HTTPException(status_code=403, detail="Cannot modify the admin role")
+    
     for key, value in role.model_dump(exclude_unset=True).items():
         setattr(db_role, key, value)
     db.commit()
@@ -166,10 +170,17 @@ def delete_role(role_id: int, db: Session = Depends(get_db), current_user: model
     if not db_role:
         raise HTTPException(status_code=404, detail="Role not found")
     
+    # Prevent deleting the admin or guest role
+    if db_role.name in ("admin", "guest"):
+        raise HTTPException(status_code=403, detail=f"Cannot delete the '{db_role.name}' role")
+    
     member_count = db.query(models.ProjectMember).filter(models.ProjectMember.role_id == role_id).count()
     if member_count > 0:
         raise HTTPException(status_code=400, detail="Role is in use by members")
     
+    # Delete role permissions first
+    db.query(RolePermission).filter(RolePermission.role_id == role_id).delete()
+    
     db.delete(db_role)
     db.commit()
     return None
@@ -185,6 +196,10 @@ def assign_permissions(role_id: int, perm_assign: PermissionAssign, db: Session
     if not role:
         raise HTTPException(status_code=404, detail="Role not found")
     
+    # Prevent modifying permissions of the admin role
+    if role.name == "admin":
+        raise HTTPException(status_code=403, detail="Cannot modify permissions of the admin role")
+    
     db.query(RolePermission).filter(RolePermission.role_id == role_id).delete()
     
     for perm_id in perm_assign.permission_ids: