Add peer progress API endpoint

[SanjanaBottu]

Description

This PR adds a backend API endpoint for the Peer Progress feature.

Endpoint:

GET /api/peer_progress/:unit_id/:student_id

The endpoint calculates and returns a student’s progress within a selected unit, including:

• student ID
• unit ID
• target grade
• completed tasks
• required tasks
• progress percentage

This backend endpoint supports the matching doubtfire-web Peer Progress frontend PR.

Tested locally by running the Rails API server and opening the endpoint in the browser.

How Has This Been Tested?

Example test URL:
http://localhost:3000/api/peer_progress/1/25

Confirmed that the endpoint returns JSON data with the expected fields:

• student_id
• unit_id
• target_grade
• tasks_completed
• tasks_required
• progress_percentage

Also tested with a project that has task records to confirm the task counts and progress percentage are calculated correctly.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• 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)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines 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 if appropriate
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have created or extended unit tests to address my new additions
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules