chore: create Multica handoff checkpoint

app/frontend/shared/base.css

@@ -125,13 +125,13 @@ dialog::backdrop {
   backdrop-filter: blur(2px);
 }
 
-@media (min-width: 721px) {
+@media (min-width: 768px) {
   body {
     overflow-y: hidden;
   }
 }
 
-@media (max-width: 720px), (max-width: 1023px) and (max-height: 600px) {
+@media (max-width: 767px), (max-width: 1023px) and (max-height: 600px) {
   html {
     width: 100%;
 
@@ -185,3 +185,28 @@ dialog::backdrop {
     animation: auto ease 0s 1 normal none running none;
   }
 }
+
+/* Mobile document contract: the page owns the only vertical scrollbar. */
+@media (max-width: 767px) {
+  html {
+    width: 100%;
+    min-width: var(--mobile-min-width);
+    min-height: 100%;
+    height: auto;
+    overflow-x: hidden;
+  }
+
+  body.mobile-shell {
+    width: 100%;
+    min-width: var(--mobile-min-width);
+    min-height: 100%;
+    height: auto;
+    padding-bottom: var(--mobile-content-bottom);
+    overflow-y: auto;
+    overscroll-behavior-y: contain;
+  }
+
+  body.mobile-shell.mobile-command-open {
+    overflow: hidden;
+  }
+}