test(github): add buildCommitClock unit tests (JhaSourav07#1157)

## Description

Fixes JhaSourav07#1058

Added focused unit tests for `buildCommitClock` to verify weekday
aggregation behavior and output structure.

## Pillar

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

## Visual Preview

Not applicable — 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): ...`).
* [ ] 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

lib/github.test.ts

@@ -6,6 +6,7 @@ import {
   fetchUserRepos,
   getFullDashboardData,
   generateAchievements,
+  buildCommitClock,
   clearGitHubApiCacheForTests,
   GITHUB_CACHE_TTL_MS,
   validateGitHubUsername,
@@ -909,6 +910,46 @@ describe('buildInsights', () => {
   });
 });
 
+describe('buildCommitClock', () => {
+  it('counts commits only on Sunday when all days are Sunday', () => {
+    const result = buildCommitClock([
+      { date: '2024-01-07', contributionCount: 3 },
+      { date: '2024-01-14', contributionCount: 2 },
+    ]);
+
+    expect(result).toHaveLength(7);
+    expect(result[0].commits).toBeGreaterThan(0);
+    expect(result.slice(1).every((item) => item.commits === 0)).toBe(true);
+  });
+
+  it('returns 7 days with zero commits for empty input', () => {
+    const result = buildCommitClock([]);
+
+    expect(result).toHaveLength(7);
+    expect(result.every((item) => item.commits === 0)).toBe(true);
+  });
+
+  it('always returns exactly 7 items', () => {
+    const result = buildCommitClock([{ date: '2024-01-07', contributionCount: 1 }]);
+
+    expect(result).toHaveLength(7);
+  });
+
+  it('uses weekday labels from Sunday to Saturday', () => {
+    const result = buildCommitClock([]);
+
+    expect(result.map((item) => item.day)).toEqual([
+      'Sun',
+      'Mon',
+      'Tue',
+      'Wed',
+      'Thu',
+      'Fri',
+      'Sat',
+    ]);
+  });
+});
+
 // ---------- EPIC ENHANCEMENT TESTS ----------
 
 describe('fetchOrgMembers', () => {