fix(ui): polish mobile layouts, error pages, and volume backups

Keep error pages full-viewport, lift the unsaved bar above the
mobile keyboard, make status/heading layouts stack cleanly on small
screens, route service DB backups to volume-backups, and tighten
volume backup grid/forms. Cover with feature tests.

tests/Feature/PreviewStatusSummaryTest.php

@@ -13,7 +13,9 @@ it('aggregates preview container and health check status', function () {
         ->toContain('Not configured')
         ->toContain('aria-label="About unconfigured health checks"')
         ->toContain('Traffic can still be routed to the container')
-        ->toContain('aria-haspopup="menu"');
+        ->toContain('aria-haspopup="menu"')
+        ->toContain('right-auto! left-0!')
+        ->toContain('w-[min(16rem,calc(100vw-1.5rem))]!');
 });
 
 it('uses the aggregated preview status in the previews list', function () {