refactor(github): extract buildCommitClock helper (JhaSourav07#752)

## Description

Fixes JhaSourav07#299

Extracted commit clock aggregation logic into `buildCommitClock()`
helper.

Added tests for:
- per-day contribution aggregation
- helper output correctness

Existing `getFullDashboardData` commitClock tests continue to pass.

## Pillar

- [x] 🛠️ Other (Bug fix, refactoring, docs)

## Visual Preview

N/A — backend refactor only.

## Checklist before requesting a review:

- [x] I have read the CONTRIBUTING.md file.
- [x] I have tested these changes locally.
- [x] I have run npm run format and npm run lint locally.
- [x] My commits follow Conventional Commits format.
- [x] I have made sure I have only one commit in this PR.

Author: JhaSourav07

lib/github.test.ts

@@ -10,6 +10,7 @@ import {
   GITHUB_CACHE_TTL_MS,
   validateGitHubUsername,
   cacheKey,
+  buildCommitClock,
 } from './github';
 import type { ContributionCalendar } from '../types';
 
@@ -562,3 +563,26 @@ describe('cacheKey', () => {
     expect(cacheKey('contributions', 'testuser')).toContain('contributions');
   });
 });
+
+describe('buildCommitClock', () => {
+  it('aggregates commits correctly by day of week', () => {
+    const allDays = [
+      { date: '2024-06-09', contributionCount: 2 }, // Sun
+      { date: '2024-06-10', contributionCount: 5 }, // Mon
+      { date: '2024-06-10', contributionCount: 3 }, // Mon
+      { date: '2024-06-12', contributionCount: 4 }, // Wed
+    ];
+
+    const result = buildCommitClock(allDays);
+
+    expect(result).toEqual([
+      { day: 'Sun', commits: 2 },
+      { day: 'Mon', commits: 8 },
+      { day: 'Tue', commits: 0 },
+      { day: 'Wed', commits: 4 },
+      { day: 'Thu', commits: 0 },
+      { day: 'Fri', commits: 0 },
+      { day: 'Sat', commits: 0 },
+    ]);
+  });
+});

lib/github.ts

@@ -1,6 +1,6 @@
 // lib/github.ts
 
-import type { ContributionCalendar } from '../types';
+import type { ContributionCalendar, ContributionDay } from '../types';
 import { calculateStreak } from './calculate';
 import { TTLCache } from './cache';
 import { LANGUAGE_COLORS } from './svg/languageColors';
@@ -365,6 +365,21 @@ export function generateAchievements(totalContributions: number, currentStreak:
   return achievements;
 }
 
+export function buildCommitClock(allDays: ContributionDay[]) {
+  const dayNames = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];
+  const dayTotals = new Array(7).fill(0);
+
+  for (const day of allDays) {
+    const dow = new Date(day.date).getUTCDay();
+    dayTotals[dow] += day.contributionCount;
+  }
+
+  return dayNames.map((name, i) => ({
+    day: name,
+    commits: dayTotals[i],
+  }));
+}
+
 export async function getFullDashboardData(username: string, options: FetchOptions = {}) {
   if (!validateGitHubUsername(username)) {
     console.warn(
@@ -518,18 +533,7 @@ export async function getFullDashboardData(username: string, options: FetchOptio
       text: `Your longest coding streak is ${streakStats.longestStreak} days!`,
     });
   }
-
-  // Aggregate real contribution data by day of week from the already-fetched calendar
-  const dayNames = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];
-  const dayTotals = new Array(7).fill(0);
-  for (const day of allDays) {
-    const dow = new Date(day.date).getUTCDay();
-    dayTotals[dow] += day.contributionCount;
-  }
-  const commitClock = dayNames.map((name, i) => ({
-    day: name,
-    commits: dayTotals[i],
-  }));
+  const commitClock = buildCommitClock(allDays);
 
   return {
     profile,