offline 스코프 제거, rp_claims 값 표준화

userfront/lib/features/auth/domain/consent_scope_policy.dart

@@ -0,0 +1,11 @@
+bool isRefreshTokenScopeAlias(String scope) {
+  final normalized = scope.trim().toLowerCase();
+  return normalized == 'offline' || normalized == 'offline_access';
+}
+
+List<String> filterConsentScopes(Iterable<String> scopes) {
+  return scopes
+      .map((scope) => scope.trim())
+      .where((scope) => scope.isNotEmpty && !isRefreshTokenScopeAlias(scope))
+      .toList(growable: false);
+}