[Backend] Real course analytics with database aggregation pipeline

[jobbykings]

Description

The analytics service (analyticsService.ts) and data aggregation service (dataAggregation.ts) currently have @ts-ignore comments and incomplete implementations. Build out real database aggregation queries that power course analytics and reporting.

Files to Modify

• backend/src/services/analyticsService.ts — Implement real aggregation queries, fix @ts-ignore
• backend/src/services/dataAggregation.ts — Build MongoDB aggregation pipeline for reports
• backend/src/controllers/analyticsController.js — Wire to real service calls
• backend/src/models/ — Add aggregation helper methods to Course, Enrollment, User models

Definition of Done

• Enrollment trend data aggregated from actual enrollment records
• Course completion rates calculated from real progress data
• Student performance metrics (avg scores, time to complete) from real quiz/submission data
• Demographic breakdowns from user profile data (aggregated, anonymized)
• All aggregation queries use database indexes for performance
• No @ts-ignore comments remain in analytics code

Acceptance Criteria

• GET /api/analytics/enrollment-trends returns real enrollment data over time
• GET /api/analytics/completion-rates returns actual completion percentages
• Analytics for specific course return that course's real metrics, not mocks
• Large date range queries complete within 2 seconds
• No PII exposed in aggregated analytics responses
• TypeScript compiles cleanly with no @ts-ignore in analytics files

[gbengaeben]

Hi Maintainer,

I’d love to work on this issue. I’ve reviewed the requirements and believe I can implement the solution according to the project’s guidelines and best practices.

If the issue is available, I’d be happy to take ownership and submit a PR for review.

Thank you for your consideration

[grantfox-oss]

🦊 GrantFox — @gbengaeben has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #26)
2. Your PR will be reviewed by the Epondia maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@gbengaeben's PR #137 was approved and merged by @jobbykings.

🏆 @gbengaeben: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (506 total points). Track your full progress on GrantFox.

👏 Great work, @gbengaeben! Keep contributing to Epondia.