[Backend][MVP] Request Resolution and Status Consistency

[berat-sayin]

Description

Ensure request resolution is supported and that request/assignment statuses remain consistent across the full MVP flow.

Scope

• Support marking request as resolved where needed
• Define valid request and assignment status transitions
• Prevent inconsistent states across create/cancel/reassign/resolve flows
• Add basic tests for flow consistency

Acceptance Criteria

• Requests can be marked as resolved where required
• Assignment and request statuses stay consistent across the flow
• Invalid transitions are prevented
• Basic MVP flow works end-to-end: availability, matching, assignment, cancellation, re-evaluation, and resolution

[berat-sayin]

Implemented in #175. Closing the issue.