fix: use relative path for subfolder starter code downloads

[mayurigade-hub]

Summary [required]

When users clicked the Download button for projects whose starter code was stored inside a subfolder (e.g. starter_code/survey_form/index.html), the server was using os.path.basename which stripped the subfolder name and only kept the filename. Flask then looked for starter_code/index.html which does not exist, resulting in a 404 error. This PR fixes the issue by using os.path.relpath to preserve the full relative path from the starter code directory.

Related Issue [required]

Closes #524

Type of Change [required]

• Bug fix — resolves a broken behaviour

What Was Changed [required]

File	Change made
routes/main_routes.py	Replaced os.path.basename with os.path.relpath in download_code route to preserve subfolder structure when serving files

How to Test This PR [required]

1. Clone this branch: git checkout fix/starter-code-subfolder-download
2. Install dependencies: pip install -r requirements.txt
3. Run the app: python app.py
4. Open http://127.0.0.1:5000
5. Navigate to Project 9 (Survey Form)
6. Click the Download button
7. File should download successfully — no 404 error
8. Repeat for a project without a subfolder to confirm nothing is broken
9. Run tests: python tests/test_basic.py

Expected test output:

27 passed, 0 failed out of 27 tests

Test Results [required]

paste output here

Self-Review Checklist [required]

• I have read CONTRIBUTING.md and followed all guidelines
• My branch name follows the convention: fix/starter-code-subfolder-download
• I have run python tests/test_basic.py and all 27 tests pass
• I have run flake8 . locally and there are no errors
• I have not introduced any print() or console.log() debug statements
• Every new function I wrote has a docstring
• I have not modified files outside the scope of the linked issue

Notes for Reviewer

The only logic change is in the download_code route inside routes/main_routes.py. The duplicate import os inside the function was also removed since os is already imported at the top of the file.

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[mayurigade-hub]

hello maintainers!

please review this PR.

Thank you!