Fix product images, add-to-cart, and add Sub Categories filter

- Add display:block to .product-card-image so padding-top aspect ratio works on anchor tags
- Add Cache-Control: no-transform header to disable Cloudflare Rocket Loader (was deferring main.js and breaking add-to-cart click handlers)
- Add Sub Categories filter row on shop page using product_types table
- Show category · sub-category on product cards
- Add Sub Categories section to footer
- Preserve subcat param across category/sort filter links

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

assets/css/style.css

@@ -338,6 +338,7 @@ img {
 }
 
 .product-card-image {
+    display: block;
     position: relative;
     padding-top: 100%;
     overflow: hidden;