feat(auth): add role/permission management (backend + frontend)

- RoleService: CRUD, assign_permissions, get_role_permissions
- PermissionService: list all tenant permissions
- Role handlers: 8 endpoints with RBAC permission checks
- Frontend Roles page: table, create/edit modal, permission assignment
- Frontend Roles API: full CRUD + permission operations
- Routes registered in AuthModule protected_routes

crates/erp-auth/src/handler/mod.rs

@@ -1,2 +1,3 @@
 pub mod auth_handler;
+pub mod role_handler;
 pub mod user_handler;