Add shipping cost management and checkout shipping fees.

Business store shipping groups/static rates UI, and customer checkout that quotes and applies shipping on delivery and payment.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/customer/src/components/checkout/CheckoutLayout.module.css

@@ -102,18 +102,20 @@
 }
 
 .container {
-  width: 60%;
-  max-width: none;
+  width: min(1040px, 96%);
   min-width: 320px;
 }
 
-@media (max-width: 900px) {
-  .container {
-    width: 90%;
-  }
+.shell {
+  display: flex;
+  align-items: stretch;
+  gap: 16px;
+  width: 100%;
 }
 
 .card {
+  flex: 1;
+  min-width: 0;
   background: var(--glass-bg);
   backdrop-filter: blur(24px);
   -webkit-backdrop-filter: blur(24px);
@@ -123,6 +125,18 @@
   padding: 28px 28px 24px;
 }
 
+@media (max-width: 900px) {
+  .container {
+    width: 94%;
+  }
+}
+
+@media (max-width: 760px) {
+  .shell {
+    flex-direction: column;
+  }
+}
+
 @media (max-width: 480px) {
   .header {
     padding: 12px 16px;