LIGHT (JhaSourav07#3423)

## Description

Adds dedicated unit tests for the light theme in
`lib/svg/themes/light.test.ts` to verify its color configuration, SVG
output, and WCAG contrast compliance.

Fixes JhaSourav07#2303

## Pillar

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

## Summary of Changes

Created `lib/svg/themes/light.test.ts` with 5 test cases:

1. **Theme exists** — asserts `themes` has a `light` key
2. **Valid hex color strings** — regex-validates `bg`, `text`, `accent`
are proper 6-char hex values
3. **Matches design spec** — exact match on `#ffffff` (bg), `#24292f`
(text), `#0969da` (accent)
4. **Hex colors appear in generated SVG** — calls `generateSVG` with
light theme params and verifies all three hex values are present in the
output
5. **WCAG AA contrast compliance** — computes relative luminance per
WCAG 2.1 and asserts `bg` vs `text` contrast ratio ≥ 4.5:1

## Visual Preview

Not applicable — this is a testing-only change with no visual output.

## 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 format` and `npm run lint` locally and
resolved all errors (CI will fail otherwise).
- [x] My commits follow the Conventional Commits format.
- [ ] I have updated `README.md` if I added a new theme or URL
parameter. (not needed)
- [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)
- [x] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

lib/svg/themes/light.test.ts

@@ -0,0 +1,64 @@
+import { describe, it, expect } from 'vitest';
+import { themes } from '../themes';
+import { generateSVG } from '../generator';
+import type { BadgeParams, ContributionCalendar, StreakStats } from '../../../types';
+import { contrastRatio } from './test-utils';
+
+describe('light theme', () => {
+  it('exists as a key in the themes object', () => {
+    expect(themes).toHaveProperty('light');
+  });
+
+  it('has valid 6-digit hex color strings (without #) for bg, text, and accent', () => {
+    const hexRegex = /^[0-9a-fA-F]{6}$/;
+
+    expect(themes.light.bg).toMatch(hexRegex);
+    expect(themes.light.text).toMatch(hexRegex);
+    expect(themes.light.accent).toMatch(hexRegex);
+  });
+
+  it('matches the defined light color values for the design spec', () => {
+    expect(themes.light.bg).toBe('ffffff');
+    expect(themes.light.text).toBe('24292f');
+    expect(themes.light.accent).toBe('0969da');
+  });
+
+  it('contains the specific light hex colors in generated SVG output', () => {
+    const mockStats: StreakStats = {
+      currentStreak: 5,
+      longestStreak: 10,
+      totalContributions: 100,
+      todayDate: '2024-06-12',
+    };
+    const mockCalendar: ContributionCalendar = {
+      totalContributions: 10,
+      weeks: [
+        {
+          contributionDays: [
+            { contributionCount: 5, date: '2024-06-11' },
+            { contributionCount: 5, date: '2024-06-12' },
+          ],
+        },
+      ],
+    };
+    const lightParams: BadgeParams = {
+      user: 'testuser',
+      bg: themes.light.bg,
+      text: themes.light.text,
+      accent: themes.light.accent,
+      speed: '8s',
+      scale: 'linear',
+    };
+
+    const svg = generateSVG(mockStats, lightParams, mockCalendar);
+
+    expect(svg).toContain(`#${themes.light.bg}`);
+    expect(svg).toContain(`#${themes.light.text}`);
+    expect(svg).toContain(`#${themes.light.accent}`);
+  });
+
+  it('provides sufficient WCAG AA contrast between background and text', () => {
+    const ratio = contrastRatio(themes.light.bg, themes.light.text);
+    expect(ratio).toBeGreaterThanOrEqual(4.5);
+  });
+});