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/style.css

@@ -1056,6 +1056,117 @@ button { font-family: inherit; cursor: pointer; border: none; background: none;
 /* Notices */
 .woocommerce-store-notice { background: var(--stamp) !important; color: var(--manila) !important; }
 
+/* ───────── Mobile nav hamburger ───────── */
+.rar-nav__toggle {
+  display: none;
+  align-items: center;
+  justify-content: center;
+  background: none;
+  border: 1px solid rgba(245, 241, 232, 0.35);
+  color: var(--manila);
+  cursor: pointer;
+  padding: 6px 10px;
+  border-radius: 2px;
+  transition: border-color 0.15s;
+}
+.rar-nav__toggle:hover { border-color: var(--stamp); color: var(--stamp); }
+.rar-nav__toggle svg { display: block; }
+/* hamburger → × swap */
+.rar-nav__toggle .icon-close { display: none; }
+.rar-nav.is-open .rar-nav__toggle .icon-open { display: none; }
+.rar-nav.is-open .rar-nav__toggle .icon-close { display: block; }
+
+/* Mobile drawer */
+.rar-nav__drawer {
+  display: none;
+  position: fixed;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  background: var(--ink);
+  z-index: 99;
+  flex-direction: column;
+  padding: 80px 32px 40px;
+  overflow-y: auto;
+}
+.rar-nav__drawer.is-open { display: flex; }
+.rar-nav__drawer a {
+  font-family: var(--mono);
+  font-size: 14px;
+  letter-spacing: 0.2em;
+  text-transform: uppercase;
+  color: var(--manila);
+  text-decoration: none;
+  padding: 18px 0;
+  border-bottom: 1px solid rgba(245, 241, 232, 0.12);
+  transition: color 0.15s;
+}
+.rar-nav__drawer a:hover { color: var(--stamp); }
+.rar-nav__drawer .rar-nav__drawer-close {
+  position: absolute;
+  top: 16px;
+  right: 20px;
+  background: none;
+  border: none;
+  color: var(--manila);
+  cursor: pointer;
+  font-size: 22px;
+  padding: 8px;
+  line-height: 1;
+}
+
+/* ───────── WooCommerce product tabs ───────── */
+.woocommerce-tabs.wc-tabs-wrapper { padding: 0; }
+.woocommerce-tabs ul.tabs,
+.woocommerce div.product .woocommerce-tabs ul.tabs {
+  list-style: none !important;
+  padding: 0 !important;
+  margin: 0 0 0 !important;
+  display: flex !important;
+  border-bottom: 2px solid var(--hairline-strong) !important;
+}
+.woocommerce-tabs ul.tabs::before,
+.woocommerce div.product .woocommerce-tabs ul.tabs::before { border: none !important; }
+.woocommerce-tabs ul.tabs li,
+.woocommerce div.product .woocommerce-tabs ul.tabs li {
+  background: transparent !important;
+  border: none !important;
+  border-bottom: 3px solid transparent !important;
+  margin-bottom: -2px !important;
+  padding: 0 !important;
+  border-radius: 0 !important;
+}
+.woocommerce-tabs ul.tabs li::before,
+.woocommerce-tabs ul.tabs li::after,
+.woocommerce div.product .woocommerce-tabs ul.tabs li::before,
+.woocommerce div.product .woocommerce-tabs ul.tabs li::after { display: none !important; }
+.woocommerce-tabs ul.tabs li.active,
+.woocommerce div.product .woocommerce-tabs ul.tabs li.active {
+  border-bottom-color: var(--stamp) !important;
+  background: transparent !important;
+}
+.woocommerce-tabs ul.tabs li a,
+.woocommerce div.product .woocommerce-tabs ul.tabs li a {
+  font-family: var(--mono) !important;
+  font-size: 11px !important;
+  letter-spacing: 0.16em !important;
+  text-transform: uppercase !important;
+  color: var(--ink-soft) !important;
+  padding: 12px 20px !important;
+  display: block !important;
+}
+.woocommerce-tabs ul.tabs li.active a,
+.woocommerce div.product .woocommerce-tabs ul.tabs li.active a { color: var(--stamp) !important; }
+.woocommerce-Tabs-panel,
+.woocommerce div.product .woocommerce-Tabs-panel {
+  padding: 28px 0 !important;
+  border: none !important;
+  font-size: 14px !important;
+  line-height: 1.7 !important;
+  color: var(--ink-soft) !important;
+}
+
 /* ───────── Responsive ───────── */
 @media (max-width: 1024px) {
   .rar-hero__grid, .rar-product-detail, .rar-cart-page { grid-template-columns: 1fr; }
@@ -1064,6 +1175,7 @@ button { font-family: inherit; cursor: pointer; border: none; background: none;
   .rar-cat-layout { grid-template-columns: 1fr; }
   .rar-filter-sidebar { display: none; }
   .rar-nav__links { display: none; }
+  .rar-nav__toggle { display: flex; }
   .rar-editorial__press { gap: 24px; }
   .rar-metrics { grid-template-columns: repeat(2, 1fr); }
   .rar-about-hero { grid-template-columns: 1fr; }