fix: improve recommendation input validation for unsupported values (#676)

[mishtiagrawal02-cloud]

Summary

This PR improves recommendation input validation by adding stricter checks for unsupported values in recommendation inputs.

Previously, validation only checked for missing fields, which allowed unsupported values (such as invalid time availability, unsupported experience levels, or unsupported interests) to reach recommendation logic and potentially cause inconsistent behavior. This update validates allowed values and returns meaningful validation errors. Additional tests were added to cover invalid input cases.

Related Issue

Closes #676

Type of Change

• Bug fix — resolves a broken behaviour
• Feature — adds new functionality
• Data — adds new projects to data/projects.json
• Documentation — updates docs, README, or code comments only
• Style — CSS or visual changes only, no logic change
• Refactor — restructures code without changing behaviour
• Test — adds or updates tests

What Was Changed

File	Change made
utils/recommender.py	Added stricter validation for unsupported values in level, interest, and time availability
tests/test_basic.py	Added test cases for invalid recommendation inputs

How to Test This PR

1. Checkout this branch:

   git checkout fix/input-validation-676
   

2. Run tests:

python tests/test_basic.py

3. Verify:

• Invalid level values are rejected
• Invalid interest values are rejected
• Invalid time availability values are rejected
• Existing valid inputs continue working

Expected result:

44 passed, 0 failed out of 44 tests

Test Results

44 passed, 0 failed out of 44 tests

Self-Review Checklist

• I have read CONTRIBUTING.md and followed guidelines
• I ran tests locally
• I have not introduced debug statements
• I have not modified unrelated files outside issue scope

Notes for Reviewer

This PR improves recommendation input validation by rejecting unsupported values and adds test coverage for invalid input cases.

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