test(api validation): check query validation boundaries for ?user= parameter (Variation 3) (JhaSourav07#2058)

## Description

Fixes JhaSourav07#1444

## Pillar

- [ ] 🎨 Pillar 1 — New Theme Design
- [ ] 📐 Pillar 2 — Geometric SVG Improvement
- [ ] 🕐 Pillar 3 — Timezone Logic Optimization
- [x] 🛠️ Other (Security / Input Validation Testing)

## Summary of Changes
- Added a query validation boundary unit test under a dedicated layout
block comment to `lib/validations.test.ts`.
- Verified that passing a simulated input string exceeding 39 characters
(`'a'.repeat(40)`) to the `?user=` parameter correctly triggers a schema
validation error containing the expected message: `'cannot exceed 39
characters'`.
- Added a complementary boundary test to confirm that a username at the
exact maximum permissible boundary limit of 39 characters
(`'a'.repeat(39)`) passes validation successfully.

## Checklist before requesting a review:

- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally using the isolated Vitest
runner.
- [x] My commits follow the Conventional Commits format (`test(api
validation): ...`).

Author: JhaSourav07

lib/validations.test.ts

@@ -1031,3 +1031,33 @@ describe('streakParamsSchema — layout query validation boundaries (Variation 2
     }
   });
 });
+
+/* ==========================================================================
+ * USER PARAMETER — QUERY VALIDATION BOUNDARIES (VARIATION 3)
+ * ========================================================================== */
+
+describe('streakParamsSchema user maxLength validation boundaries (Variation 3)', () => {
+  it('rejects a GitHub username that exceeds the 39 character length threshold', () => {
+    const invalidPayload = {
+      user: 'a'.repeat(40),
+    };
+
+    const parseResult = streakParamsSchema.safeParse(invalidPayload);
+
+    expect(parseResult.success).toBe(false);
+    if (!parseResult.success) {
+      const fieldErrors = parseResult.error.flatten().fieldErrors;
+      expect(fieldErrors.user).toBeDefined();
+      expect(fieldErrors.user?.[0]).toContain('cannot exceed 39 characters');
+    }
+  });
+
+  it('accepts a username exactly at the upper limit of 39 characters', () => {
+    const validPayload = {
+      user: 'a'.repeat(39),
+    };
+
+    const parseResult = streakParamsSchema.safeParse(validPayload);
+    expect(parseResult.success).toBe(true);
+  });
+});