add frontend AES-GCM and base64 helpers with Vitest coverage.

frontend/vitest.config.ts

@@ -0,0 +1,17 @@
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { defineConfig } from 'vitest/config';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+export default defineConfig({
+    resolve: {
+        alias: {
+            '@': path.resolve(__dirname, 'src')
+        }
+    },
+    test: {
+        environment: 'node',
+        include: ['src/**/*.spec.ts']
+    }
+});