add contextual prompts for skipped setup steps

Disable checkout when Stripe isn't connected (cart drawer, cart page,
and early guard in checkout controller to prevent orphaned orders).
Show amber warning on order detail when email isn't configured.
Fix pre-existing missing vertical spacing between page blocks.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

assets/css/shop/components.css

@@ -1022,6 +1022,9 @@
     max-width: 80rem;
     margin-inline: auto;
     padding: 2rem 1rem;
+    display: flex;
+    flex-direction: column;
+    gap: 2rem;
   }
 
   /* ── Shop container (body-level defaults) ── */
@@ -1528,6 +1531,17 @@
     cursor: pointer;
     font-family: var(--t-font-body);
     margin-bottom: 0.5rem;
+
+    &:disabled {
+      opacity: 0.5;
+      cursor: not-allowed;
+    }
+  }
+
+  .cart-drawer-notice {
+    font-size: var(--t-text-sm);
+    color: var(--t-text-secondary);
+    text-align: center;
   }
 
   /* ── Cart item row ── */
@@ -1864,6 +1878,13 @@
     text-align: center;
   }
 
+  .order-summary-notice {
+    font-size: var(--t-text-sm);
+    color: var(--t-text-secondary);
+    text-align: center;
+    margin-bottom: 0.75rem;
+  }
+
   /* ── Content body ── */
 
   .content-body {