Fix mobile hamburger menu, designs page template, product tab styling, and stock field (REPA-78)

- Add mobile hamburger toggle button and full-screen nav drawer (≤1024px)
- Fix product tab styles: complete tab CSS without relying on WC parent selectors; explicit wc-single-product enqueue on product pages
- Fix STOCK field: conditionally hide when get_stock_quantity() returns null instead of showing '— units'
- Add page-designs.php template + template_include filter so /designs/ uses themed layout instead of raw WooCommerce output
- Align nav/footer terminology: 'Canvas' → 'Wall Decor' in nav fallback; correct broken category URL slugs (mugs→drinkware, canvas→wall-decor, planners→stationery, blog→the-memo); add 'Bulk / HR' to mobile drawer

Co-Authored-By: Paperclip <noreply@paperclip.ing>

theme/js/rar.js

@@ -176,6 +176,26 @@
     } catch (e) {}
   }
 
+  // ─── Mobile nav drawer toggle ────────────────────────────────────────────────
+  window.rarToggleNav = function () {
+    var nav = document.getElementById('rar-nav');
+    var drawer = document.getElementById('rar-nav-drawer');
+    var toggle = document.getElementById('rar-nav-toggle');
+    if (!drawer) return;
+    var isOpen = drawer.classList.contains('is-open');
+    drawer.classList.toggle('is-open', !isOpen);
+    if (nav) nav.classList.toggle('is-open', !isOpen);
+    if (toggle) toggle.setAttribute('aria-expanded', isOpen ? 'false' : 'true');
+    document.body.style.overflow = isOpen ? '' : 'hidden';
+  };
+
+  document.addEventListener('keydown', function (e) {
+    if (e.key === 'Escape') {
+      var drawer = document.getElementById('rar-nav-drawer');
+      if (drawer && drawer.classList.contains('is-open')) { rarToggleNav(); }
+    }
+  });
+
   // ─── Search overlay toggle ───────────────────────────────────────────────────
   window.rarToggleSearch = function () {
     var overlay = document.getElementById('rar-search-overlay');