As a participant I should be prevented from altering a day sheet if it was confirmed

[x-snackage-x]

Estimate S Storypoints

Tasks Checklist

• [x] BE: At Timestamp participant post check confirmed flag of day sheet
• [x] BE: return 403 Forbidden if day sheet is confirmed and block post
• [x] FE: inform User of error with appropriate message

Acceptance Criteria

• Confirmed day sheets cannot be changed by participant
• rejection reason is obvious to user

Non-Functional Requirements Non

Dependencies Non