Backend: Delete assessment

GitHub Issue: #216

Backend task for deleting an assessment (DELETE /assessments/{assessmentId}) – soft delete, check permissions and status rules, implement, and verify against the spec.

Docs: Assessment list (Actions menu → Ukloni assessment, Delete confirmation modal) Spec: DELETE /assessments/{assessmentId} (deleteAssessment), AssessmentConflict in api-docs/openapi.yaml DB: Assessments (DeletedAt) in api/database/create_schema.sql

1. Double check API spec and DB structure

• Soft delete (decided): the spec soft-deletes (sets DeletedAt) and keeps candidates, board members, grades and notes. Data is kept for 2 years (see Data retention). BTC školovanje and BTC certificiranje use the same approach.
• Rule: only upcoming assessments can be deleted → 409 assessment_not_upcoming. Check the docs agree.
• After deleting, every assessment endpoint (detail, edit, forms, notes overviews, results) → 404, and the list excludes it.
• Roles and permissions: Trainer only (assessments.edit). Check against the docs permission table.

2. Implementation

• Roles and permissions: require assessments.edit → 403.
• DB: set DeletedAt (and UpdatedAt). Make sure the shared “load assessment” helper used by the other endpoints filters DeletedAt IS NULL.
• Function + repository. Status check → 409. Unknown or already deleted id → 404. Success → 204.

3. Verify implementation against spec

• Status codes and the error value match deleteAssessment.
• Active / past assessment → 409. Evaluator → 403. Deleting twice → 404 the second time.
• After deleting: list excludes it; detail, forms and results → 404; the rows are still in the database.

Done when

A trainer can delete an upcoming assessment, and it disappears everywhere in the app while its data stays in the database.