test: add coverage for AUTO_THEME_LIGHT and AUTO_THEME_DARK exports (JhaSourav07#1214)

## Description

Adds test coverage for the renamed auto theme exports to ensure they
continue referencing the correct theme objects.

## Changes
Extended lib/svg/themes.test.ts
Added test verifying AUTO_THEME_LIGHT === themes.light
Added test verifying AUTO_THEME_DARK === themes.dark
Added test verifying AUTO_THEME_LIGHT.bg === themes.light.bg
Added test verifying AUTO_THEME_DARK.accent === themes.dark.accent

Fixes JhaSourav07#1075 

## Pillar

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



## 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 community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

lib/svg/themes.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest';
-import { themes } from './themes';
+import { themes, AUTO_THEME_LIGHT, AUTO_THEME_DARK } from './themes';
 
 describe('themes', () => {
   it('should not use # prefix in background colors', () => {
@@ -19,4 +19,19 @@ describe('themes', () => {
       expect(theme.accent.startsWith('#')).toBe(false);
     });
   });
+  it('AUTO_THEME_LIGHT references themes.light', () => {
+    expect(AUTO_THEME_LIGHT).toBe(themes.light);
+  });
+
+  it('AUTO_THEME_DARK references themes.dark', () => {
+    expect(AUTO_THEME_DARK).toBe(themes.dark);
+  });
+
+  it('AUTO_THEME_LIGHT bg matches themes.light.bg', () => {
+    expect(AUTO_THEME_LIGHT.bg).toBe(themes.light.bg);
+  });
+
+  it('AUTO_THEME_DARK accent matches themes.dark.accent', () => {
+    expect(AUTO_THEME_DARK.accent).toBe(themes.dark.accent);
+  });
 });