Added testcase for contribution intensity mapping (JhaSourav07#805)

## Description

Added tests verifying contribution count to intensity mapping in
`lib/github.test.ts`.

Fixes JhaSourav07#689 

## 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 change)

## 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.
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standard (no raw elements, smooth animations, correct fonts).
- [x] (Recommended) I joined the CommitPulse Discord server for faster
collaboration, mentorship, and PR support.

## Tested mappings

- 0 -> 0
- 2 -> 1
- 5 -> 2
- 8 -> 3
- 15 -> 4

Author: JhaSourav07

lib/github.test.ts

@@ -328,6 +328,61 @@ describe('getFullDashboardData', () => {
     expect(totalClockCommits).toBe(8); // 3 + 0 + 5 from mockCalendar
   });
 
+  it('maps contribution counts to correct intensity levels', async () => {
+    const intensityCalendar: ContributionCalendar = {
+      totalContributions: 30,
+      weeks: [
+        {
+          contributionDays: [
+            { contributionCount: 0, date: '2024-06-10' },
+            { contributionCount: 2, date: '2024-06-11' },
+            { contributionCount: 5, date: '2024-06-12' },
+            { contributionCount: 8, date: '2024-06-13' },
+            { contributionCount: 15, date: '2024-06-14' },
+          ],
+        },
+      ],
+    };
+
+    vi.mocked(fetch).mockImplementation(async (url: any) => {
+      if (typeof url === 'string' && url.includes('/users/octocat/repos')) {
+        return mockResponse([]);
+      }
+
+      if (typeof url === 'string' && url.includes('/users/octocat')) {
+        return mockResponse({
+          login: 'octocat',
+          name: 'The Octocat',
+          avatar_url: 'avatar.png',
+          public_repos: 0,
+          followers: 0,
+          following: 0,
+          created_at: '2020-01-01T00:00:00Z',
+        });
+      }
+
+      return mockResponse({
+        data: {
+          user: {
+            contributionsCollection: {
+              contributionCalendar: intensityCalendar,
+            },
+          },
+        },
+      });
+    });
+
+    const result = await getFullDashboardData('octocat');
+
+    const activities = result.activity;
+
+    expect(activities[0].intensity).toBe(0);
+    expect(activities[1].intensity).toBe(1);
+    expect(activities[2].intensity).toBe(2);
+    expect(activities[3].intensity).toBe(3);
+    expect(activities[4].intensity).toBe(4);
+  });
+
   it('throws if profile fetch fails', async () => {
     vi.mocked(fetch).mockImplementation(async (url: any) => {
       if (typeof url === 'string' && url.includes('/users/octocat/repos')) {