test(LanguageChart): add massive scaling coverage (JhaSourav07#3619)

## Description

Fixes # (issue number)

## Pillar

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

## Visual Preview
## Description

Fixes JhaSourav07#2564

Added comprehensive massive-scaling test coverage for `LanguageChart` to
verify stability and rendering behavior under extremely large datasets
and high metric values.

## 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.
* [x] I have run `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 (not applicable — test-only change).
* [ ] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

## Tests Added

* Verifies rendering with massive language datasets.
* Tests extremely large percentage values.
* Validates gradient generation under heavy load.
* Confirms layout stability with high-volume entries.
* Checks rendering performance remains within acceptable limits.

## Verification

* ✅ 5 test cases added
* ✅ Vitest passes
* ✅ Lint passes
* ✅ No runtime crashes under large datasets

## Checklist before requesting a review:

- [ ] I have read the `CONTRIBUTING.md` file.
- [ ] I have tested these changes locally
(`localhost:3000/api/streak?user=YOUR_USERNAME`).
- [ ] I have run `npm run format` and `npm run lint` locally and
resolved all errors (CI will fail otherwise).
- [ ] 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.
- [ ] I have started the repo.
- [ ] 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).
- [ ] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

components/dashboard/LanguageChart.massive-scaling.test.tsx

@@ -0,0 +1,69 @@
+import { render, screen } from '@testing-library/react';
+import { describe, expect, it, vi } from 'vitest';
+
+import LanguageChart, { buildGradientStops } from './LanguageChart';
+
+class MockIntersectionObserver implements IntersectionObserver {
+  readonly root: Element | Document | null = null;
+  readonly rootMargin: string = '';
+  readonly thresholds: ReadonlyArray<number> = [];
+
+  disconnect = vi.fn();
+  observe = vi.fn();
+  takeRecords = vi.fn(() => []);
+  unobserve = vi.fn();
+}
+
+global.IntersectionObserver = MockIntersectionObserver;
+
+const massiveLanguages = Array.from({ length: 1000 }, (_, index) => ({
+  name: `Language-${index}`,
+  percentage: Number((100 / 1000).toFixed(2)),
+  color: `#${(index + 100000).toString(16).slice(0, 6)}`,
+}));
+
+describe('LanguageChart massive scaling', () => {
+  it('renders without crashing for massive language dataset', () => {
+    render(<LanguageChart languages={massiveLanguages} />);
+
+    expect(screen.getByText('Top Languages')).toBeInTheDocument();
+    expect(screen.getAllByText('Language-0').length).toBeGreaterThan(0);
+  });
+
+  it('renders high-volume language labels safely', () => {
+    render(<LanguageChart languages={massiveLanguages} />);
+
+    expect(screen.getByText('Language-10')).toBeInTheDocument();
+    expect(screen.getByText('Language-999')).toBeInTheDocument();
+  });
+
+  it('handles extremely large percentage values without runtime failure', () => {
+    const highMetricLanguages = [
+      { name: 'TypeScript', percentage: 999999, color: '#3178c6' },
+      { name: 'JavaScript', percentage: 888888, color: '#f7df1e' },
+      { name: 'Python', percentage: 777777, color: '#3572A5' },
+    ];
+
+    render(<LanguageChart languages={highMetricLanguages} />);
+
+    expect(screen.getAllByText('TypeScript').length).toBeGreaterThan(0);
+    expect(screen.getAllByText('999999%').length).toBeGreaterThan(0);
+  });
+
+  it('keeps gradient stop generation stable for massive data', () => {
+    const gradientStops = buildGradientStops(massiveLanguages);
+
+    expect(gradientStops).toContain('#');
+    expect(gradientStops.length).toBeGreaterThan(1000);
+  });
+
+  it('renders massive dataset within acceptable performance limits', () => {
+    const start = performance.now();
+
+    render(<LanguageChart languages={massiveLanguages} />);
+
+    const end = performance.now();
+
+    expect(end - start).toBeLessThan(500);
+  });
+});