Implemented phase 5 for the POC prototype in the Website service.

Services/Website/Resources/Static/css/sign-in.css

@@ -69,6 +69,31 @@
   gap: var(--space-7);
 }
 
+/* The backup-passkey nudge on first sign-in */
+.gate__nudge {
+  display: flex;
+  align-items: flex-start;
+  gap: var(--space-3);
+  padding: var(--space-4);
+  border-radius: var(--radius-sm);
+  background: var(--header);
+  color: var(--on-dark-muted);
+  font-size: 13px;
+  line-height: 1.45;
+}
+
+.gate__nudge .icon {
+  margin-top: 1px;
+  color: var(--gold);
+}
+
+.gate__nudge-title {
+  margin-bottom: 3px;
+  color: var(--on-dark);
+  font-size: 14px;
+  font-weight: 600;
+}
+
 .gate__demo {
   display: flex;
   flex-direction: column;