test(scroll-restoration): add ScrollRestoration component test suite (JhaSourav07#3100)

## Description

Adds a complete test suite for ScrollRestoration.

- Verifies component mounts successfully
- Restores saved scroll position from sessionStorage
- Persists scroll position during scroll events
- Handles missing saved positions correctly
- Cleans up scroll listeners on unmount

Fixes JhaSourav07#2286 

## Pillar

- [x] 📐 Pillar 2 — Geometric SVG Improvement
- [x] 🛠️ Other (Bug fix, refactoring, docs)


## 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.
- [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

app/components/ScrollRestoration.test.tsx

@@ -0,0 +1,83 @@
+import { render, cleanup } from '@testing-library/react';
+import '@testing-library/jest-dom/vitest';
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import ScrollRestoration from './ScrollRestoration';
+
+const mockUsePathname = vi.fn();
+
+vi.mock('next/navigation', () => ({
+  usePathname: () => mockUsePathname(),
+}));
+
+describe('ScrollRestoration', () => {
+  const scrollToMock = vi.fn();
+  const addEventListenerSpy = vi.spyOn(window, 'addEventListener');
+  const removeEventListenerSpy = vi.spyOn(window, 'removeEventListener');
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+
+    mockUsePathname.mockReturnValue('/dashboard');
+
+    Object.defineProperty(window, 'scrollTo', {
+      writable: true,
+      value: scrollToMock,
+    });
+
+    sessionStorage.clear();
+  });
+
+  afterEach(() => {
+    cleanup();
+  });
+
+  it('mounts cleanly without crashing', () => {
+    const { container } = render(<ScrollRestoration />);
+
+    expect(container).toBeDefined();
+  });
+
+  it('restores saved scroll position on mount', () => {
+    sessionStorage.setItem('scroll-position-/dashboard', '250');
+
+    render(<ScrollRestoration />);
+
+    expect(scrollToMock).toHaveBeenCalledWith(0, 250);
+  });
+
+  it('registers scroll listener and saves scroll position', () => {
+    render(<ScrollRestoration />);
+
+    expect(addEventListenerSpy).toHaveBeenCalledWith('scroll', expect.any(Function));
+
+    Object.defineProperty(window, 'scrollY', {
+      writable: true,
+      configurable: true,
+      value: 500,
+    });
+
+    const handler = addEventListenerSpy.mock.calls.find(
+      ([event]) => event === 'scroll'
+    )?.[1] as EventListener;
+
+    handler(new Event('scroll'));
+
+    expect(sessionStorage.getItem('scroll-position-/dashboard')).toBe('500');
+  });
+
+  it('does not scroll when no saved position exists', () => {
+    render(<ScrollRestoration />);
+
+    expect(scrollToMock).not.toHaveBeenCalled();
+  });
+
+  it('removes scroll listener on unmount', () => {
+    const { unmount } = render(<ScrollRestoration />);
+
+    const handler = addEventListenerSpy.mock.calls.find(([event]) => event === 'scroll')?.[1];
+
+    unmount();
+
+    expect(removeEventListenerSpy).toHaveBeenCalledWith('scroll', handler);
+  });
+});