polish: add responsive breakpoints for nav, home, and shop

src/components/Nav.module.css

@@ -31,3 +31,13 @@
   text-decoration: none;
   color: var(--color-charcoal);
 }
+
+@media (max-width: 640px) {
+  .nav {
+    flex-direction: column;
+    gap: var(--space-sm);
+  }
+  .links {
+    gap: var(--space-md);
+  }
+}

src/pages/Home.module.css

@@ -51,3 +51,13 @@
 .banner a {
   color: var(--color-gold);
 }
+
+@media (max-width: 640px) {
+  .headline {
+    font-size: 2.2rem;
+  }
+  .row {
+    flex-direction: column;
+    align-items: center;
+  }
+}

src/pages/Shop.module.css

@@ -26,3 +26,9 @@
   grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
   gap: var(--space-lg);
 }
+
+@media (max-width: 640px) {
+  .grid {
+    grid-template-columns: 1fr;
+  }
+}