test(validation): check query validation boundaries for accent param (JhaSourav07#1944)

## Description

Fixes JhaSourav07#1442
Program: GSSoC 2026

This PR handles the implementation of validation boundary unit testing
for the incoming `?accent=` query parameter under variation 2.

Previously, basic parameter checking was evaluated, but checking extreme
bounds for incorrect color hex syntax combinations required isolated
boundary test coverage to guarantee input schema safety.

### Changes Made

* Added 1 target schema validation boundary test case inside
`lib/validations.test.ts`.
* Mocked an invalid parameter payload passing an accent color string
configuration value set to `'#ZZZZZZ'`.
* Asserted that the system validation layer catches the hex syntax
violation and processes it correctly according to the repository's
parsing bounds.

### Why this matters

Secures internal configuration mapping engines against structural
failures when handling malformed custom color styles, guaranteeing that
invalid hex inputs cannot compromise SVG output generation parameters.

## Pillar

- [ ] 🎨 Pillar 1 — New Theme Design
- [ ] 📐 Pillar 2 — Geometric SVG Improvement
- [ ] 🕐 Pillar 3 — Timezone Logic Optimization
- [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 (`npm run test`).
- [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 server for faster
collaboration, mentorship, and PR support.

Author: JhaSourav07

lib/validations.test.ts

@@ -740,6 +740,20 @@ describe('streakParamsSchema — accent parameter HEX color validation', () => {
     expect(result.success).toBe(false);
   });
 
+  it('rejects the invalid boundary hex color "#ZZZZZZ" for accent', () => {
+    const result = streakParamsSchema.safeParse({
+      user: 'octocat',
+      accent: '#ZZZZZZ',
+    });
+
+    expect(result.success).toBe(false);
+    if (!result.success) {
+      expect(result.error.issues[0]?.message).toContain(
+        'accent must be a valid 3 or 6 character hex color without #'
+      );
+    }
+  });
+
   it('accepts a valid 6-character hex color for accent', () => {
     const result = streakParamsSchema.safeParse({
       user: 'octocat',