Add/edit/remove/test federation peers from Settings in both UIs, applied live.
Web gets RwLock<Vec<Arc<RemoteClient>>> + dedicated /api/remotes PUT/test
endpoints; passwords masked/write-only on the web (kept-by-URL on blank save),
shown in the clear on the local desktop.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
