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.

resources/css/app.css

@@ -1016,8 +1016,14 @@ html[data-theme="custom"] textarea:disabled {
 }
 
 /* Public error surfaces (401/404/500/…). Match auth shell canvas + accent. */
+.error-page-body {
+    width: 100vw;
+    height: 100dvh;
+    overflow: hidden;
+}
+
 .error-shell {
-    min-height: 100dvh;
+    height: 100%;
     display: flex;
     align-items: center;
     justify-content: center;
@@ -2375,6 +2381,11 @@ input[type="search"]::-webkit-search-results-decoration {
     grid-template-columns: 7.5rem minmax(9rem, 1fr) 8rem 6rem 5rem minmax(9rem, 1fr) minmax(9rem, auto);
 }
 
+.volume-backup-executions-grid {
+    grid-template-columns: 7.5rem minmax(0, 1fr) 8.5rem 7rem 9rem minmax(9rem, 0.7fr);
+    min-width: 50rem;
+}
+
 .clone-destinations-table-grid {
     grid-template-columns: 2rem minmax(10rem, 1fr) minmax(10rem, 1fr);
 }