Roll out refined-minimal styling and product thumbnails across pages

Apply the dashboard's refined direction to the rest of the app:
- Items: page-title header, product thumbnail (best-price image) beside
  each item name via the shared thumbSm component.
- Results: refined headers; per-item and global tables get standardized
  thumbnails (global table gains a thumbnail column).
- Settings: page-title + subtitle, section headings restyled.
- Item form: page-title header.
- Shared: thumbSm component + compact thumbnail CSS variant.

templates/item_form.templ

@@ -136,11 +136,11 @@ func newCategory(v string, known []string) string {
 
 templ itemFormBody(d ItemFormData) {
 	<div>
-		<h1 class="text-3xl font-semibold mb-6">
+		<h1 class="v-page-title mb-6">
 			if d.IsEdit {
 				Edit { d.Item.Name }
 			} else {
-				Add Item
+				Add item
 			}
 		</h1>
 		if len(d.Errors) > 0 {