Phase 2: Create admin UI for system configuration
- Add new /admin/settings route in frontend.go (protected by AdminMiddleware)
- Create admin_settings.templ with HTMX-powered form for base URL
- Add Settings link to admin sidebar navigation
- Admin settings form submits via HTMX to PUT /api/system/config
- Success message displays after save with updated form
The settings page allows admins to configure the base URL used for
device sync URLs, OPDS endpoints, and API access.