Add test coverage for work item states API endpoints

[BenGWeeks]

Summary

Add unit tests for the new Azure DevOps work item states API endpoints introduced in PR #169.

Related PR

• Resolve GitHub issue 150 (Kanban) #169

Endpoints to test

1. GET /api/devops/workitem-states - Fetches available work item states from Azure DevOps
2. PATCH /api/devops/tickets/[id]/state - Updates a ticket's state

Suggested test scenarios

workitem-states endpoint

• Returns states for configured work item types
• Handles missing/unauthorized Azure DevOps access gracefully
• Caches state responses appropriately

state update endpoint

• Successfully updates ticket state
• Handles invalid state transitions
• Returns appropriate error for non-existent tickets
• Validates authorization

Notes

This was identified during code review on PR #169 and deferred to keep the PR focused.