- Replace the server-computed settings flag with prAuthAvailable and document it in shared Settings types
- Compute PR auth availability from gh CLI auth first, with GITHUB_TOKEN as fallback in GET /api/settings
- Rename dashboard settings state/props/hooks from githubTokenConfigured to prAuthAvailable and strip server-owned auth fields on save
- Update PR section messaging to guide users to run 'gh auth login' and refresh related route/component tests