feat(auth): add bootstrap token flow for initial admin creation

- Introduced `BootstrapService` to handle admin creation when no admins exist.
- Added `/auth/bootstrap-admin` endpoint to consume bootstrap tokens.
- Updated `RbacRepository` to support counting admins and assigning roles.
- Included unit tests for `BootstrapService` to ensure token behavior and admin assignment.

backend/src/auth/rbac.service.ts

@@ -51,4 +51,12 @@ export class RbacService implements OnApplicationBootstrap {
 	async getUserPermissions(userId: string) {
 		return this.rbacRepository.findPermissionsByUserId(userId);
 	}
+
+	async countAdmins() {
+		return this.rbacRepository.countAdmins();
+	}
+
+	async assignRoleToUser(userId: string, roleSlug: string) {
+		return this.rbacRepository.assignRole(userId, roleSlug);
+	}
 }