test: verify boundary robustness of tracking event dispatchers JhaSourav07#1550 (JhaSourav07#1712)

## Description

Fixes JhaSourav07#1550

## Pillar

- [ ] 🎨 Pillar 1 — New Theme Design
- [ ] 📐 Pillar 2 — Geometric SVG Improvement
- [ ] 🕐 Pillar 3 — Timezone Logic Optimization
- [x] 🛠️ Other (Bug fix, refactoring, docs)

## Visual Preview
Added a brand new robust Vitest unit validation block ensuring
empty/falsy inputs gracefully terminate and prevent faulty tracking
dispatches. Verified all 478 tests passing locally.

## Checklist before requesting a review:

- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally
(`localhost:3000/api/streak?user=YOUR_USERNAME`).
- [x] I have run `npm run format` and `npm run lint` locally and
resolved all errors (CI will fail otherwise).
- [x] My commits follow the Conventional Commits format (e.g.,
`feat(themes): ...`, `fix(calculate): ...`).
- [x] I have updated `README.md` if I added a new theme or URL
parameter.
- [x] I have started the repo.
- [x] I have made sure that i have only one commit to merge in this PR.
- [x] The SVG output matches the CommitPulse "premium quality" aesthetic
standard (no raw elements, smooth animations, correct fonts).
- [x] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

utils/tracking.test.ts

@@ -159,4 +159,20 @@ describe('trackUser', () => {
       configurable: true,
     });
   });
+
+  it('gracefully bypasses tracking when user metric logs are empty or falsy', () => {
+    const fetchMock = vi.fn().mockResolvedValue({});
+    vi.stubGlobal('fetch', fetchMock);
+
+    const sendBeaconMock = vi.fn().mockReturnValue(true);
+    Object.defineProperty(navigator, 'sendBeacon', {
+      value: sendBeaconMock,
+      configurable: true,
+    });
+
+    trackUser('');
+
+    expect(sendBeaconMock).not.toHaveBeenCalled();
+    expect(fetchMock).not.toHaveBeenCalled();
+  });
 });

utils/tracking.ts

@@ -1,4 +1,7 @@
 export function trackUser(username: string) {
+  if (!username || username.trim() === '') {
+    return;
+  }
   if (typeof navigator === 'undefined' || typeof window === 'undefined') return;
   if (!username) return;