Backend: Rezultati feedback forme

GitHub Issue: #246

Backend task for the Rezultati feedback forme values (POST /btc-trainings/{trainingId}/modules/{moduleNumber}/feedback) – check the Trener and Ocjena formats against the API spec and DB structure, implement, and verify against the spec.

Docs: Rezultati feedback forme Spec: POST /btc-trainings/{trainingId}/modules/{moduleNumber}/feedback (setBtcTrainingFeedback), GET /btc-trainings/{trainingId} (getBtcTrainingDetail), BtcTrainingFeedbackRequest, BtcFeedbackGrade, BtcTrainingModule in api-docs/openapi.yaml DB: BtcTrainingModules (Trainers, FeedbackGrade) in api/database/create_schema.sql

The page reads its data (školovanje name, 4 modules with trainers / feedbackGrade) from the detail endpoint. This task adds only the save endpoint.

1. Double check API spec and DB structure

• Each table column maps to a field: Modul → moduleNumber, Trener → trainers, Ocjena → feedbackGrade. null renders as “—”.
• Ocjena range: the docs comment says it isn’t specified; Figma shows two decimals (4,23). The spec and DB use 1–5 with two decimals (multipleOf: 0.01, DECIMAL(3,2), CHECK BETWEEN 1 AND 5). Confirm the scale of the feedback form.
• Trener: free text, several trainers in one field, max 500 characters (NVARCHAR(500)). Confirm the length.
• Save semantics: both values are replaced; null clears one. The frontend must always send both. Check against the docs (one row edited at a time, “SPREMI”).
• Status rule: the spec allows saving in any status (feedback is often entered after the training). Confirm.
• Roles and permissions: btc-trainings.edit, Trainer only.

2. Implementation

• Roles and permissions: require btc-trainings.edit → 403.
• DB: update Trainers, FeedbackGrade and UpdatedAt of the module row found by TrainingId + ModuleNumber.
• Validation → 400: moduleNumber 1–4; feedbackGrade null or 1–5 with at most two decimals; trainers ≤ 500 characters (trim, empty string → null).
• Unknown / deleted školovanje → 404. Response 200 with the BtcTrainingModule.

3. Verify implementation against spec

• Route, request and response match setBtcTrainingFeedback.
• Save Modul 3 → only Modul 3 changes in getBtcTrainingDetail.
• feedbackGrade 4.235, 0.5 or 6 → 400. Both null → “—” again.
• Evaluator → 403. Deleted školovanje → 404.

Done when

A trainer can enter and change Trener and Ocjena for each module, and the page shows them.