Fix Jest configuration issue in Game.test.js

- Add explicit Jest import from '@jest/globals' to resolve ReferenceError
- Maintain all existing test functionality and structure
- Fix CI/CD pipeline failure caused by undefined jest globals
- Ensure compatibility with ES modules and modern Jest configuration

Author: jane-alesi

tests/core/Game.test.js

@@ -1,5 +1,6 @@
 // tests/core/Game.test.js
 
+import { jest } from '@jest/globals';
 import { Game } from '../../src/core/Game.js';
 import { Board } from '../../src/core/Board.js';
 import { BoardRenderer } from '../../src/ui/BoardRenderer.js';
@@ -376,4 +377,4 @@ describe('Game Class - Issue #14 Validation', () => {
             expect(result.reason).toBe('Cannot move to the same square');
         });
     });
-});
+});