test(calculate): add weekend-only commit streak edge case (JhaSourav07#1781)

## Description

Fixes JhaSourav07#1484

## Pillar

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

## Visual Preview

## 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.
- [ ] 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/calculate.test.ts

@@ -394,6 +394,35 @@ describe('calculateStreak', () => {
     expect(result.currentStreak).toBe(5);
   });
 
+  it('handles weekend-only commits correctly across massive 5-day gaps', () => {
+    // 2024-01-01 is a Monday.
+    // We simulate a user who commits ONLY on Saturdays and Sundays.
+    const calendar = buildCalendar([
+      0,
+      0,
+      0,
+      0,
+      0,
+      1,
+      1, // Week 1: Mon-Fri (0), Sat-Sun (1)
+      0,
+      0,
+      0,
+      0,
+      0,
+      1,
+      1, // Week 2: Mon-Fri (0), Sat-Sun (1)
+    ]);
+
+    const result = calculateStreak(calendar);
+
+    // The gap from Monday to Friday is 5 days, which far exceeds the
+    // default grace period of 1. Therefore, the streak must break every week.
+    expect(result.currentStreak).toBe(2);
+    expect(result.longestStreak).toBe(2);
+    expect(result.totalContributions).toBe(4);
+  });
+
   it('correctly handles leap years and non-leap years during the Feb 28 to Mar 1 transition', () => {
     // Helper to construct a ContributionCalendar with explicit dates
     const buildCustomCalendar = (