[BUG]: [Improvement] Add regression test for /get_mcq_answer response contract consistency

[Ashvin-KS]

Bug Description

Description

After the fix in PR #590, /get_mcq_answer now correctly returns the output key for invalid/mismatched input cases.
However, there is no automated regression test to enforce this response contract, so future refactors could silently reintroduce the old outputs key or break the invalid-input behavior.

Proposed Solution

Add a backend regression test that validates the invalid-input contract for /get_mcq_answer:

• response contains output
• response does not contain outputs
• response value is an empty list for mismatched question/options lengths

Expected Behavior

The API contract remains stable over time, and CI catches regressions immediately if response keys or invalid-input behavior change.

Steps to Reproduce

1. Start the backend server locally.
2. Send a POST request to /get_mcq_answer with mismatched input sizes:
   • input_question with 2 entries
   • input_options with 1 entry
3. Observe current behavior returns empty output.
4. Note that without regression coverage, this contract can be accidentally broken in future changes without automated detection.

Logs and Screenshots

N/A (contract/regression coverage gap; no runtime crash required)

Environment Details

• OS: Windows 11
• Backend: Python/Flask (EduAid backend)
• Endpoint: /get_mcq_answer
• Context: Follow-up to PR fix(backend): standardize /get_mcq_answer output key #590 contract standardization

Impact

Medium - Feature works but has issues

Code of Conduct

• I have joined the Discord server and will post updates there
• I have searched existing issues to avoid duplicates