Add course enrollment flow — Enroll button that calls backend and contract

[Anuoluwapo25]

Description

There is no enrollment flow in the UI. Learners cannot enroll in a course from the frontend — clicking a course just opens the viewer but does not register the learner on-chain or in the backend.

What Needs to Be Done

1. Add an "Enroll" button to the course detail / course card view
2. On click:
   • Call CourseMilestone.enroll(learner, courseId) on-chain via the connected wallet
   • Call POST /api/enrollments to record enrollment in the backend
3. After enrollment, redirect to the first lesson
4. Show "Enrolled" badge if already enrolled (check is_enrolled())
5. Gate lesson content behind enrollment check

Acceptance Criteria

• Enrollment recorded on-chain
• Enrollment recorded in backend DB
• Cannot enroll twice (contract + UI guard)
• Enrolled learner sees "Continue" instead of "Enroll"

Files Affected

• src/components/CourseCard.tsx
• src/hooks/useEnrollment.ts (create)
• server/src/routes/enrollments.routes.ts (create)

Labels

frontend, backend, integration, help wanted, Stellar Wave

[Wetshakat]

Hi maintainer
I will like to work on this issue eta 4hrs

[playmaker410]

Hi Maintainer,

I’d love to take this on. I have hands-on experience with Rust, Soroban, Cairo, and TypeScript, and I’m confident I can deliver a solid solution within 24 hours.