feat: retain search term and results, and fix thread safety issues

Release 0.5.1

Release 0.5.0

git commit -m "Update appcast for v0.4.0"

feat: add Sparkle auto-update support

- Add UpdateService.swift for Sparkle integration
- Add Check for Updates menu command
- Configure Info.plist with SUFeedURL and SUPublicEDKey
- Enable Hardened Runtime for distribution
- Add release.sh helper script for generating appcast
- Add initial appcast.xml for v1.0

fix: add missing await in AgentDetailView for uninstallSkill

fix: add write permissions for release workflow