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/dashboard.templ

@@ -209,6 +209,16 @@ templ thumb(url, source string) {
 	}
 }
 
+// thumbSm is the compact table-row variant of thumb (no source placeholder
+// glyph — a plain quiet square when an item has no best-price image yet).
+templ thumbSm(url string) {
+	if url != "" {
+		<img class="v-thumb v-thumb-sm" src={ url } loading="lazy" alt="" referrerpolicy="no-referrer"/>
+	} else {
+		<div class="v-thumb v-thumb-sm v-thumb-empty"></div>
+	}
+}
+
 func resultMeta(r ResultRow) string {
 	if r.Title != "" {
 		return r.Title