test(svg-constants-type-compiler): verify TypeScript Compiler Validation & Schema Constraints Stability (JhaSourav07#3229)

## Description
Creates lib/svg/constants.type-compiler.test.ts with 5 type-level tests
using Vitest's expectTypeOf to assert that all exported constants from
lib/svg/constants.ts carry the correct TypeScript types at compile time.

**Tests:**

1. Numeric dimension constants (SVG_WIDTH, SVG_HEIGHT, GHOST_HEIGHT_PX,
MAX_LOG_HEIGHT, MAX_LINEAR_HEIGHT) are typed as number
2. Scale multiplier constants (LOG_SCALE_MULTIPLIER,
LINEAR_SCALE_MULTIPLIER) are typed as number
3. FONT_MAP is typed as Record<string, string> — not Record<string,
number> or any wider type
4. CONTRIBUTION_MILESTONES is typed as number[] with numeric elements
5. All numeric constants satisfy a number parameter constraint —
verifying they can be passed to any function expecting number without
type errors

Fixes JhaSourav07#2892

## 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

## 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/constants.type-compiler.test.ts

@@ -0,0 +1,48 @@
+import { describe, expectTypeOf, it } from 'vitest';
+import {
+  CONTRIBUTION_MILESTONES,
+  FONT_MAP,
+  GHOST_HEIGHT_PX,
+  LINEAR_SCALE_MULTIPLIER,
+  LOG_SCALE_MULTIPLIER,
+  MAX_LINEAR_HEIGHT,
+  MAX_LOG_HEIGHT,
+  SVG_HEIGHT,
+  SVG_WIDTH,
+} from './constants';
+
+describe('lib/svg/constants — TypeScript type compiler', () => {
+  it('numeric dimension constants are typed as number', () => {
+    expectTypeOf(SVG_WIDTH).toBeNumber();
+    expectTypeOf(SVG_HEIGHT).toBeNumber();
+    expectTypeOf(GHOST_HEIGHT_PX).toBeNumber();
+    expectTypeOf(MAX_LOG_HEIGHT).toBeNumber();
+    expectTypeOf(MAX_LINEAR_HEIGHT).toBeNumber();
+  });
+
+  it('scale multiplier constants are typed as number', () => {
+    expectTypeOf(LOG_SCALE_MULTIPLIER).toBeNumber();
+    expectTypeOf(LINEAR_SCALE_MULTIPLIER).toBeNumber();
+  });
+
+  it('FONT_MAP satisfies Record<string, string> — keys and values are both strings', () => {
+    expectTypeOf(FONT_MAP).toEqualTypeOf<Record<string, string>>();
+    expectTypeOf(FONT_MAP).not.toEqualTypeOf<Record<string, number>>();
+  });
+
+  it('CONTRIBUTION_MILESTONES satisfies a readonly number array and its elements are numbers', () => {
+    expectTypeOf(CONTRIBUTION_MILESTONES).toEqualTypeOf<number[]>();
+    expectTypeOf(CONTRIBUTION_MILESTONES).items.toBeNumber();
+  });
+
+  it('a function accepting number accepts all numeric constants without type errors', () => {
+    const requiresNumber = (n: number): number => n;
+
+    expectTypeOf(requiresNumber).parameter(0).toBeNumber();
+    // Verify each constant satisfies the number parameter type
+    expectTypeOf(SVG_WIDTH).toEqualTypeOf<Parameters<typeof requiresNumber>[0]>();
+    expectTypeOf(SVG_HEIGHT).toEqualTypeOf<Parameters<typeof requiresNumber>[0]>();
+    expectTypeOf(LOG_SCALE_MULTIPLIER).toEqualTypeOf<Parameters<typeof requiresNumber>[0]>();
+    expectTypeOf(LINEAR_SCALE_MULTIPLIER).toEqualTypeOf<Parameters<typeof requiresNumber>[0]>();
+  });
+});