test(svg): verify all supported themes produce valid SVG output (JhaSourav07#2038)

## Description

Fixes JhaSourav07#719

## Pillar

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

## Visual Preview

N/A — Test suite addition. No user interface or SVG layout modifications
were made.

## 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 starred 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

lib/svg/generator.test.ts

@@ -14,6 +14,7 @@ import {
 } from './generator';
 import type { BadgeParams, ContributionCalendar, StreakStats, MonthlyStats } from '../../types';
 import { hexColor } from './sanitizer';
+import { themes } from './themes';
 
 describe('generateSVG', () => {
   const mockStats: StreakStats = {
@@ -868,6 +869,29 @@ describe('generateSVG', () => {
       expect(svg).not.toContain('ABCDEFGHIJKLMNOPQRSTUVWXYZ');
     });
   });
+
+  describe('verify all supported themes produce valid SVG output', () => {
+    it('generates a valid SVG and contains the theme accent color for each supported theme', () => {
+      for (const theme of Object.values(themes)) {
+        const svg = generateSVG(
+          mockStats,
+          {
+            user: 'octocat',
+            bg: theme.bg,
+            text: theme.text,
+            accent: theme.accent,
+            speed: '8s',
+            scale: 'linear',
+          } as unknown as BadgeParams,
+          mockCalendar
+        );
+
+        expect(svg).toContain('<svg');
+        expect(svg).toContain('</svg>');
+        expect(svg.toLowerCase()).toContain(theme.accent.toLowerCase());
+      }
+    });
+  });
 });
 
 describe('generateMonthlySVG', () => {