feat: OAuth login, app dashboard, Catppuccin Mocha theme
- Add AT Protocol OAuth 2.0 login flow (PAR, DPoP, JWT client assertions)
- Resolve handles to DIDs, discover PDS and auth server metadata
- Scan user repos via com.atproto.repo.describeRepo with DPoP auth
- Display discovered AT Protocol apps in CSS masonry grid
- Map known NSID prefixes to app names, icons, and descriptions
- Single-page layout: login screen or dashboard with logout
- Catppuccin Mocha dark theme with custom Tailwind tokens
- Remove Dioxus template boilerplate (blog, echo, hero, navbar)
- Server functions for all AT Protocol operations
- Backend OAuth state persistence in server-side HashMap
- DPoP nonce retry for token endpoint
Dependencies: atproto-identity, atproto-oauth, reqwest (server-only)