add base padding to themed-input and fix contact form selector

themed-input had no padding in the base style, so inputs were rendering
with browser-default 1px/2px padding. Added 0.5rem 0.75rem as the base.

Also fixed the contact form CSS which was targeting .shop-input (a class
that doesn't exist on rendered elements) instead of .themed-input.

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

assets/css/shop/components.css

@@ -1679,8 +1679,7 @@
     color: var(--t-text-primary);
   }
 
-  .contact-form .shop-input,
-  .contact-form .shop-textarea {
+  .contact-form .themed-input {
     width: 100%;
     padding: 0.5rem 1rem;
   }