test: add ShareButtons accessibility coverage (JhaSourav07#3158)

## Description

Adds accessibility test coverage for `ShareButtons.tsx`.

Tests added:
- Verifies LinkedIn share link has an accessible aria-label.
- Verifies X/Twitter share link has an accessible aria-label.
- Verifies social media icons are marked as decorative.
- Verifies external links open securely in a new tab.
- Ensures accessibility-related attributes are present and correctly
configured.

Fixes JhaSourav07#2766

## 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.
- [ ] 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

components/ShareButtons.accessibility.test.tsx

@@ -0,0 +1,69 @@
+import { render, screen } from '@testing-library/react';
+import { describe, expect, it } from 'vitest';
+
+import ShareButtons from './ShareButtons';
+
+describe('ShareButtons accessibility behavior', () => {
+  const url = 'https://example.com';
+  const title = 'Test Title';
+
+  const renderShareButtons = () => render(<ShareButtons url={url} title={title} />);
+
+  it('provides an accessible label for the LinkedIn share link', () => {
+    renderShareButtons();
+
+    const link = screen.getByRole('link', {
+      name: 'Share on LinkedIn (opens in a new tab)',
+    });
+
+    expect(link).toBeTruthy();
+  });
+
+  it('provides an accessible label for the X/Twitter share link', () => {
+    renderShareButtons();
+
+    const link = screen.getByRole('link', {
+      name: 'Share on X / Twitter (opens in a new tab)',
+    });
+
+    expect(link).toBeTruthy();
+  });
+
+  it('marks social media icons as decorative', () => {
+    const { container } = renderShareButtons();
+
+    const icons = container.querySelectorAll('svg[aria-hidden="true"]');
+
+    expect(icons).toHaveLength(2);
+  });
+
+  it('opens LinkedIn share link in a new tab securely', () => {
+    renderShareButtons();
+
+    const link = screen.getByRole('link', {
+      name: 'Share on LinkedIn (opens in a new tab)',
+    });
+
+    expect(link.getAttribute('target')).toBe('_blank');
+
+    const rel = link.getAttribute('rel') ?? '';
+
+    expect(rel).toContain('noopener');
+    expect(rel).toContain('noreferrer');
+  });
+
+  it('opens X/Twitter share link in a new tab securely', () => {
+    renderShareButtons();
+
+    const link = screen.getByRole('link', {
+      name: 'Share on X / Twitter (opens in a new tab)',
+    });
+
+    expect(link.getAttribute('target')).toBe('_blank');
+
+    const rel = link.getAttribute('rel') ?? '';
+
+    expect(rel).toContain('noopener');
+    expect(rel).toContain('noreferrer');
+  });
+});