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

frontend/src/utils/crypto/generateDek.spec.ts

@@ -0,0 +1,19 @@
+import { describe, expect, it } from 'vitest';
+import { AES_GCM_KEY_BYTE_LENGTH } from '@/consts/crypto/aesGcmKeyByteLength';
+import { generateDek } from '@/utils/crypto/generateDek';
+
+describe('generateDek', () => {
+    it('returns a 32-byte raw AES-256 key', () => {
+        const dek = generateDek();
+
+        expect(dek).toBeInstanceOf(Uint8Array);
+        expect(dek.byteLength).toBe(AES_GCM_KEY_BYTE_LENGTH);
+    });
+
+    it('generates distinct DEKs across calls', () => {
+        const dekA = generateDek();
+        const dekB = generateDek();
+
+        expect(dekA).not.toEqual(dekB);
+    });
+});