test(layoutConstants): create layoutConstants tests (JhaSourav07#1192)

## Description

Fixes JhaSourav07#1015

Added a new test file for `lib/svg/layoutConstants.ts` covering all
exported layout constants.

Tests included:

* `GHOST_HEIGHT_PX === 4`
* `LOG_SCALE_MULTIPLIER === 12`
* `LINEAR_SCALE_MULTIPLIER === 5`
* `MAX_LOG_HEIGHT === 80`
* `MAX_LINEAR_HEIGHT === 50`

## 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 change)

## 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`).
* [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): ...`).
* [ ] 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: JhaSourav07

lib/svg/layoutConstants.test.ts

@@ -0,0 +1,30 @@
+import { describe, it, expect } from 'vitest';
+import {
+  GHOST_HEIGHT_PX,
+  LOG_SCALE_MULTIPLIER,
+  LINEAR_SCALE_MULTIPLIER,
+  MAX_LOG_HEIGHT,
+  MAX_LINEAR_HEIGHT,
+} from './layoutConstants';
+
+describe('layoutConstants', () => {
+  it('GHOST_HEIGHT_PX equals 4', () => {
+    expect(GHOST_HEIGHT_PX).toBe(4);
+  });
+
+  it('LOG_SCALE_MULTIPLIER equals 12', () => {
+    expect(LOG_SCALE_MULTIPLIER).toBe(12);
+  });
+
+  it('LINEAR_SCALE_MULTIPLIER equals 5', () => {
+    expect(LINEAR_SCALE_MULTIPLIER).toBe(5);
+  });
+
+  it('MAX_LOG_HEIGHT equals 80', () => {
+    expect(MAX_LOG_HEIGHT).toBe(80);
+  });
+
+  it('MAX_LINEAR_HEIGHT equals 50', () => {
+    expect(MAX_LINEAR_HEIGHT).toBe(50);
+  });
+});