Improve streamer reassignment UI

[sayhiben]

Summary

• replace streamer reassignment details dropdown with a stable popover and autocomplete input
• guard table reflow while reassign panel is open to preserve focus
• preload streamers in admin streams index to reduce N+1

Testing

• make lint

[github-actions]

🤖 PR Validation Summary

Status: ✅ All checks passed

Test Results

• Unit Tests: ✅ Passed
• Integration Tests: ✅ Passed

Code Quality

• Linting: ✅ Passed
• Security: ✅ Passed

View detailed results