userfront&backend test coverage 추가

userfront/test/runtime_env_compile_time_test.dart

@@ -42,5 +42,15 @@ void main() {
       expect(runtimeBackendUrl(), isNot(endsWith('/')));
       expect(runtimeUserfrontUrl(), isNot(endsWith('/')));
     });
+
+    test(
+      'sanitizedUrl removes dollar signs, whitespace, and trailing slash',
+      () {
+        expect(
+          sanitizedUrl('  https://example.test/path/\$  '),
+          'https://example.test/path',
+        );
+      },
+    );
   });
 }