Style: Apply wishlist button style to all cart buttons

Changed cart 'Proceed to Checkout' button from btn-primary-full
to btn-outline to match wishlist button style.

All cart buttons now use btn-outline (purple outlined style):
- Proceed to Checkout: btn-primary-full → btn-outline
- Continue Shopping: already btn-outline

Files updated:
- shop.html
- contact.html
- product.html
- about.html

Cart buttons now have consistent wishlist-style appearance.

website/public/about.html

@@ -116,7 +116,7 @@
                     <span class="summary-label">Subtotal:</span>
                     <span class="summary-value" id="cartSubtotal">$0.00</span>
                   </div>
-                  <a href="/checkout" class="btn-primary-full"
+                  <a href="/checkout" class="btn-outline"
                     >Proceed to Checkout</a
                   >
                   <a href="/shop" class="btn-outline">Continue Shopping</a>

website/public/contact.html

@@ -124,7 +124,7 @@
                     <span class="summary-label">Subtotal:</span>
                     <span class="summary-value" id="cartSubtotal">$0.00</span>
                   </div>
-                  <a href="/checkout" class="btn-primary-full"
+                  <a href="/checkout" class="btn-outline"
                     >Proceed to Checkout</a
                   >
                   <a href="/shop" class="btn-outline">Continue Shopping</a>

website/public/product.html

@@ -150,7 +150,7 @@
                   <span class="summary-label">Subtotal:</span>
                   <span class="summary-value" id="cartSubtotal">$0.00</span>
                 </div>
-                <a href="/checkout" class="btn-primary-full"
+                <a href="/checkout" class="btn-outline"
                   >Proceed to Checkout</a
                 >
                 <a href="/shop" class="btn-outline">Continue Shopping</a>

website/public/shop.html

@@ -681,7 +681,7 @@
                     <span class="summary-label">Subtotal:</span>
                     <span class="summary-value" id="cartSubtotal">$0.00</span>
                   </div>
-                  <a href="/checkout" class="btn-primary-full"
+                  <a href="/checkout" class="btn-outline"
                     >Proceed to Checkout</a
                   >
                   <a href="/shop" class="btn-outline">Continue Shopping</a>