test(svg): add tests for auto-theme SVG dark palette (JhaSourav07#634)

## Description

Fixes JhaSourav07#389

## Pillar

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

## Visual Preview
No visual changes, just adding tests.

## 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 server for faster
collaboration, mentorship, and PR support.

Author: JhaSourav07

lib/svg/generator.test.ts

@@ -204,13 +204,13 @@ describe('generateSVG', () => {
       expect(svg).toContain('--cp-accent: #0969da');
     });
 
-    it('injects @media (prefers-color-scheme: dark) with dark palette', () => {
+    it('injects @media (prefers-color-scheme: dark) with exact dark palette hex values', () => {
       const svg = generateSVG(mockStats, autoParams, mockCalendar);
 
       // Media query block must be present
       expect(svg).toContain('prefers-color-scheme: dark');
 
-      // Dark-mode CSS variables inside the media query
+      // Check for exact hex values used in AUTO_DARK_THEME
       expect(svg).toContain('--cp-bg: #0d1117');
       expect(svg).toContain('--cp-text: #c9d1d9');
       expect(svg).toContain('--cp-accent: #58a6ff');