chore: add UI styles and update documentation

- Add cart drawer and product gallery thumbnail CSS
- Remove redundant type="text/javascript" attribute
- Update image optimization plan to reflect completion

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

assets/css/app.css

@@ -115,3 +115,23 @@
 @import "./theme-semantic.css";
 
 /* This file is for your main application CSS */
+
+/* Cart drawer open state styles */
+.cart-drawer.open {
+  right: 0 !important;
+}
+
+.cart-drawer-overlay.open {
+  opacity: 1 !important;
+  visibility: visible !important;
+}
+
+/* Product gallery thumbnail styles */
+.pdp-thumbnail {
+  border: 2px solid var(--t-border-default);
+  transition: border-color 0.15s ease;
+}
+
+.pdp-thumbnail-active {
+  border-color: hsl(var(--t-accent-h) var(--t-accent-s) var(--t-accent-l));
+}