Settings screen now splits responsibilities:
- Backend URL + API key move into a Test/Save popup dialog
(backend_config_dialog.dart), reachable via a "Re-configure" action.
Per M3 the Test button is left-aligned (neutral) with Cancel/Save
grouped trailing. On first run the dialog auto-opens non-dismissible.
- The screen shows the connection read-only (URL plain, key masked with
reveal) in a "Backend connection" card, and groups Theme + Push into an
"App settings" card. Theme and push apply immediately, no Save button.
- Align all card titles to titleLarge across home/status/settings.
Adds a test seam (dioBuilderForTesting) so reconfigure keeps the mock Dio
in widget tests instead of issuing real requests.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
