test(crypto): add generateMasterKey test coverage

- Add test for base64 string output
- Add test for 32-byte key length
- Add test for uniqueness

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/tests/lib/crypto-utils.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect, beforeEach, vi } from 'vitest';
-import { arrayToBase64, base64ToArray, deriveKey, encrypt, decrypt } from '../../src/lib/crypto-utils';
+import { arrayToBase64, base64ToArray, deriveKey, encrypt, decrypt, generateMasterKey } from '../../src/lib/crypto-utils';
 
 describe('crypto-utils', () => {
   describe('arrayToBase64', () => {
@@ -75,4 +75,25 @@ describe('crypto-utils', () => {
       expect(decrypted).toBe(plaintext);
     });
   });
+
+  describe('generateMasterKey', () => {
+    it('should return a base64 string', () => {
+      const key = generateMasterKey();
+      expect(typeof key).toBe('string');
+      // Base64 regex pattern
+      expect(key).toMatch(/^[A-Za-z0-9+/]+=*$/);
+    });
+
+    it('should generate 32 bytes (256 bits)', () => {
+      const key = generateMasterKey();
+      const decoded = base64ToArray(key);
+      expect(decoded.length).toBe(32);
+    });
+
+    it('should generate unique values on each call', () => {
+      const key1 = generateMasterKey();
+      const key2 = generateMasterKey();
+      expect(key1).not.toBe(key2);
+    });
+  });
 });