test(github): verify joinedDate format and stats mapping in getFullDa… (JhaSourav07#809)

## Description
Fixes JhaSourav07#687
Fixes JhaSourav07#688

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

## Visual Preview
N/A — test-only PR, no SVG output changes

## 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): ...`).
- [ ] 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
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Author: JhaSourav07

lib/github.test.ts

@@ -361,6 +361,72 @@ describe('getFullDashboardData', () => {
       '[GitHub API] Failed to fetch profile for user "octocat"'
     );
   });
+
+  it('formats joinedDate as MMM YYYY', async () => {
+    // Verifies that created_at from the REST API is formatted with toLocaleDateString('en-US')
+    // into a stable 'Jan 2020' shape regardless of the runtime environment's system locale.
+    vi.mocked(fetch).mockImplementation(async (url: any) => {
+      if (typeof url === 'string' && url.includes('/users/testuser/repos')) {
+        return mockResponse([]);
+      }
+      if (typeof url === 'string' && url.includes('/users/testuser')) {
+        return mockResponse({
+          login: 'testuser',
+          name: 'Test User',
+          avatar_url: 'https://example.com/avatar.png',
+          bio: null,
+          location: null,
+          public_repos: 0,
+          followers: 0,
+          following: 0,
+          created_at: '2020-01-15T00:00:00Z',
+        });
+      }
+      return mockResponse({
+        data: { user: { contributionsCollection: { contributionCalendar: mockCalendar } } },
+      });
+    });
+
+    const result = await getFullDashboardData('testuser');
+
+    // 'en-US' locale with { month: 'short', year: 'numeric' } always produces 'Jan 2020'
+    expect(result.profile.joinedDate).toMatch(/^[A-Za-z]+ \d{4}$/);
+  });
+
+  it('maps calculateStreak output correctly to stats', async () => {
+    // Verifies that getFullDashboardData correctly pipes the contribution calendar
+    // through calculateStreak and maps the result onto the returned stats object.
+    vi.mocked(fetch).mockImplementation(async (url: any) => {
+      if (typeof url === 'string' && url.includes('/users/testuser/repos')) {
+        return mockResponse([]);
+      }
+      if (typeof url === 'string' && url.includes('/users/testuser')) {
+        return mockResponse({
+          login: 'testuser',
+          name: 'Test User',
+          avatar_url: 'https://example.com/avatar.png',
+          bio: null,
+          location: null,
+          public_repos: 0,
+          followers: 0,
+          following: 0,
+          created_at: '2020-01-15T00:00:00Z',
+        });
+      }
+      return mockResponse({
+        data: { user: { contributionsCollection: { contributionCalendar: mockCalendar } } },
+      });
+    });
+
+    const result = await getFullDashboardData('testuser');
+
+    // totalContributions must be passed through unchanged from the calendar
+    expect(result.stats.totalContributions).toBe(mockCalendar.totalContributions);
+    // streak values are non-negative by definition
+    expect(result.stats.currentStreak).toBeGreaterThanOrEqual(0);
+    // peak (longestStreak) can never be less than the current streak
+    expect(result.stats.peakStreak).toBeGreaterThanOrEqual(result.stats.currentStreak);
+  });
 });
 
 describe('GitHub API cache behavior', () => {