Okcode/auth settings providers (#420)

* Add provider availability settings and picker filtering

- Move provider readiness checks to on-demand config loading
- Add authentication settings for Codex, Claude, and OpenClaw
- Filter thread/provider pickers to only show selectable providers

* Improve provider status loading and settings availability

- Scope provider health dependencies explicitly
- Fetch server config earlier in chat view
- Tidy provider selection and settings formatting

Author: BunsDev