fix: resolve TypeScript errors in CI type-check

- next.config.ts: cssChunking 'loose' → false ('loose' not in type)
- ActivityFeed.test.tsx: remove always-truthy TS2872 literal expression

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

app/__tests__/components/ActivityFeed.test.tsx

@@ -58,7 +58,7 @@ describe('ActivityFeed NaN Handling', () => {
     });
 
     it('should convert gaming.name to string safely', () => {
-      const validName = String('Test Game' || '');
+      const validName = String('Test Game');
       expect(validName).toBe('Test Game');
       expect(typeof validName).toBe('string');