test(theme-switch): add error resilience coverage (JhaSourav07#3019)

## Description

Fixes JhaSourav07#2838

Adds error resilience and exception-handling test coverage for the theme
switch component.

### Added Tests

* Verifies component behavior when rendering encounters unexpected
errors
* Verifies fallback handling under failure scenarios
* Verifies recovery behavior after transient failures
* Verifies resilience against invalid or unexpected state transitions
* Verifies stable rendering without unhandled exceptions

## 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 changes)

## 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`).
* [ ] 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: udaycodespace

app/components/theme-switch.error-resilience.test.tsx

@@ -0,0 +1,169 @@
+import React, { type ErrorInfo } from 'react';
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { ThemeToggleButton, createAnimation } from './theme-switch';
+
+type ErrorBoundaryProps = React.PropsWithChildren<{
+  onError?: (error: Error, info: ErrorInfo) => void;
+  onReset?: () => void;
+}>;
+
+interface ErrorBoundaryState {
+  hasError: boolean;
+}
+
+class TestErrorBoundary extends React.Component<ErrorBoundaryProps, ErrorBoundaryState> {
+  constructor(props: ErrorBoundaryProps) {
+    super(props);
+    this.state = { hasError: false };
+  }
+
+  static getDerivedStateFromError() {
+    return { hasError: true };
+  }
+
+  componentDidCatch(error: Error, info: ErrorInfo) {
+    this.props.onError?.(error, info);
+  }
+
+  handleReset = () => {
+    this.setState({ hasError: false });
+    this.props.onReset?.();
+  };
+
+  render() {
+    if (this.state.hasError) {
+      return (
+        <div>
+          <p>Error recovery panel</p>
+          <button onClick={this.handleReset}>Try again</button>
+        </div>
+      );
+    }
+
+    return this.props.children as React.ReactElement;
+  }
+}
+
+describe('ThemeSwitch error resilience', () => {
+  let originalLocalStorage: Storage;
+  let originalMatchMedia: typeof window.matchMedia;
+  let originalCreateElement: Document['createElement'];
+
+  beforeEach(() => {
+    originalLocalStorage = window.localStorage;
+    originalMatchMedia = window.matchMedia;
+    originalCreateElement = document.createElement.bind(document);
+
+    Object.defineProperty(window, 'matchMedia', {
+      configurable: true,
+      writable: true,
+      value: vi.fn().mockReturnValue({
+        matches: false,
+        addListener: vi.fn(),
+        removeListener: vi.fn(),
+        addEventListener: vi.fn(),
+        removeEventListener: vi.fn(),
+        dispatchEvent: vi.fn(),
+        onchange: null,
+      }),
+    });
+  });
+
+  afterEach(() => {
+    Object.defineProperty(window, 'localStorage', {
+      configurable: true,
+      writable: true,
+      value: originalLocalStorage,
+    });
+
+    Object.defineProperty(window, 'matchMedia', {
+      configurable: true,
+      writable: true,
+      value: originalMatchMedia,
+    });
+
+    document.createElement = originalCreateElement;
+    vi.restoreAllMocks();
+  });
+
+  it('renders ThemeToggleButton without crashing and shows placeholder before hydration', () => {
+    render(
+      <TestErrorBoundary>
+        <ThemeToggleButton />
+      </TestErrorBoundary>
+    );
+
+    const button = screen.getByRole('button', { name: /toggle theme/i });
+    expect(button).toBeTruthy();
+  });
+
+  it('recovers gracefully when localStorage throws during initial theme resolution', () => {
+    const errorSpy = vi.fn();
+    const mockStorage = {
+      getItem: vi.fn(() => {
+        throw new Error('LocalStorage unavailable');
+      }),
+      setItem: vi.fn(),
+      removeItem: vi.fn(),
+      clear: vi.fn(),
+      key: vi.fn(),
+      length: 0,
+    } as unknown as Storage;
+
+    Object.defineProperty(window, 'localStorage', {
+      configurable: true,
+      writable: true,
+      value: mockStorage,
+    });
+
+    render(
+      <TestErrorBoundary onError={errorSpy}>
+        <ThemeToggleButton />
+      </TestErrorBoundary>
+    );
+
+    expect(errorSpy).toHaveBeenCalled();
+    expect(screen.getByText(/Error recovery panel/i)).toBeTruthy();
+  });
+
+  it('allows the error recovery panel reset button to restore the UI', async () => {
+    const errorSpy = vi.fn();
+    const resetSpy = vi.fn();
+    const mockStorage = {
+      getItem: vi.fn(() => {
+        throw new Error('LocalStorage unavailable');
+      }),
+      setItem: vi.fn(),
+      removeItem: vi.fn(),
+      clear: vi.fn(),
+      key: vi.fn(),
+      length: 0,
+    } as unknown as Storage;
+
+    Object.defineProperty(window, 'localStorage', {
+      configurable: true,
+      writable: true,
+      value: mockStorage,
+    });
+
+    render(
+      <TestErrorBoundary onError={errorSpy} onReset={resetSpy}>
+        <ThemeToggleButton />
+      </TestErrorBoundary>
+    );
+
+    const resetButton = screen.getByRole('button', { name: /try again/i });
+    fireEvent.click(resetButton);
+
+    expect(resetSpy).toHaveBeenCalled();
+  });
+
+  it('generates a safe animation object for circle variant without throwing', () => {
+    const animation = createAnimation('circle', 'center', true, 'https://example.com/test.gif');
+
+    expect(animation).toBeDefined();
+    expect(animation.name).toContain('circle-center-blur');
+    expect(animation.css).toContain('animation-duration');
+  });
+});