Add API request behavior tests

[HitanshiThakar]

Description

Added focused unit tests for frontend API request behavior covering the exported API functions from frontend/src/api.ts.

Created api.request-behavior.test.ts to cover:

successful API responses
non-OK HTTP responses
timeout and abort behavior
timeout cleanup during rejected requests

Also added fake timer usage and proper mock/timer restoration to avoid test leakage.

Related Issues

Closes #471

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

Ran npx vitest run testing/unit/api.request-behavior.test.ts
7 tests passed

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.

[HitanshiThakar]

The added API request behavior tests are passing locally.
The remaining CI failures appear unrelated to this PR and are coming from existing frontend/backend tests after syncing with the latest main.

[utksh1]

The API behavior tests need a rebase/fix before review can continue. Current required checks are failing, including frontend-checks, and backend jobs are skipped. Please rebase on the current CI baseline and make the tests pass cleanly.