feat: redesign config screen for ModMenu, remove /atproto config/gui
AtProtoConfigScreen is now a proper settings panel with all
ClientPreferences fields exposed:
- Authentication section (login/logout with status)
- Sync consent toggles (stats, sessions, achievements, server status)
- Sync frequency cycle buttons (1/5/10/15/30/60/120/240 min)
- UI preferences (notifications, F3 status, compact layout)
- Privacy settings (encrypted storage, clear on logout)
- Reset to Defaults button
Removes /atproto config and /atproto gui commands — ModMenu is
now the canonical entry point for settings. Help text updated
to point to Mod Menu instead.