Set up the full OAuth flow for AT Protocol login:
- Create src/lib/atproto.ts with configureOAuth, login/resume/callback helpers,
and exported publicClient (unauthenticated) + rpc (authenticated) clients
- Add /oauth/callback route to handle the OAuth redirect
- Update left sidebar in +page.svelte with login form / logged-in state
- Update +page.js to use authenticated client when available
- Configure Vite with loopback client_id for local development on 127.0.0.1:12520

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>