test(validation): check query validation boundaries for user max length (JhaSourav07#1887)

## Description

Fixes JhaSourav07#1452
Program: GSSoC 2026

This PR handles the implementation of edge validation boundary unit
tests for the incoming `?user=` query parameters.

Previously, basic existence formatting was evaluated, but precise length
bounds were missing test coverage. This patch checks constraint
robustness against long string payloads.

### Changes Made

* Added 1 specific schema validation boundary test case inside
`lib/validations.test.ts`.
* Mocked a boundary payload passing a username input string length of 40
characters using `'a'.repeat(40)`.
* Asserted that validation handles the error structure and responds
exactly with the boundary constraint message: `'cannot exceed 39
characters'`.

### Why this matters

Secures internal endpoint ingestion routers from parsing massive string
parameters, mitigating resource exploitation vectors or unexpected error
bubble-ups down the call stack during upstream fetching operations.

---

## 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`).
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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.
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- [x] I have made sure that i have only one commit to merge in this PR.
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Author: JhaSourav07

lib/validations.test.ts

@@ -252,6 +252,17 @@ describe('streakParamsSchema', () => {
     }
   });
 
+  it('should reject user values longer than 39 characters', () => {
+    const result = streakParamsSchema.safeParse({
+      user: 'a'.repeat(40),
+    });
+
+    expect(result.success).toBe(false);
+    if (!result.success) {
+      expect(result.error.issues[0]?.message).toContain('cannot exceed 39 characters');
+    }
+  });
+
   it('should fail when user is whitespace-only input', () => {
     const result = streakParamsSchema.safeParse({
       user: '   ',