connect assessment handlers to repositories

[adarshm11]

Wire Up Assessment Handlers to Real Repos

Handler logic and the service layer are fully implemented — internal/handlers/assessments.go and internal/core/services/assessment_service.go have working validation, error handling, and business logic. The only missing piece is wiring real repository implementations into the service at startup.

---

Already done

• CreateAssessment, ListAssessments, GetAssessment, AddQuestion, AddTestCases handlers — complete with input validation and error mapping
• AssessmentService — complete with validation logic, type checking, ownership enforcement
• SetAssessmentService() function exists for DI
• Routes registered in main.go

Remaining work

• In cmd/server/main.go: instantiate the concrete Assessment, Question, and TestCase repos (from issue 02) with the DB pool
• In cmd/server/main.go: create AssessmentService via services.NewAssessmentService(assessmentRepo, questionRepo, testCaseRepo)
• In cmd/server/main.go: call handlers.SetAssessmentService(svc) before starting the server

That's it — ~5 lines of code.

Note: this requires issue #18 to be completed first.