feat(matching): match results as a scoped templ partial + enriched matches

- BookMatch now carries title/author/cover (the fields the old client
  renderer always assumed but the API never sent — cards would have
  shown 'undefined'); filled during the family-lens pass in QueryBooks
- new partial route GET /unlinked-books/matches renders the scoped
  match cascade server-side; searchMatches swaps it via htmx.ajax
  instead of rebuilding cards from JSON
- NOTE: the unlinked-books surface is currently dark end-to-end — the
  templ page has no route, the live linking.ts renderer targets a
  container no template has, and its Link button calls a
  window.showMatchModal that does not exist. This commit ships the
  scoped backend + partial; wiring the UI is a product decision.

templates/unlinked_books.templ

@@ -1,5 +1,53 @@
 package templates
 
+import (
+	"fmt"
+
+	"bookhoard/internal/services"
+)
+
+
+// UnlinkedMatchCards renders the match candidates for one device file's
+// "find matches" reveal — the /unlinked-books/matches partial response.
+// Cards are clicked through the delegated data-action handler (rendering
+// ownership: templ renders, JS only swaps and handles the click).
+templ UnlinkedMatchCards(progressId string, matches []services.BookMatch) {
+	if len(matches) == 0 {
+		<p class="text-sm text-center p-4" style="color: var(--text-secondary)">No matches found. Try manual linking.</p>
+	} else {
+		for _, match := range matches {
+			<div class="card p-4 rounded-lg border cursor-pointer hover:shadow-lg transition-shadow"
+				style="background-color: var(--bg-primary); border-color: var(--border);"
+				data-action="auto-link"
+				data-progress-id={ progressId }
+				data-media-item-id={ match.MediaItemID.String() }
+				data-confidence={ fmt.Sprintf("%v", match.Confidence) }
+			>
+				<div class="flex gap-4">
+					<img
+						src={ match.CoverImagePath }
+						alt="Cover"
+						class="w-16 h-24 object-cover rounded"
+						onerror="this.src='/static/placeholder-book.svg'"
+					/>
+					<div>
+						<h5 class="font-semibold" style="color: var(--text-primary)">{ match.Title }</h5>
+						if match.Author != "" {
+							<p class="text-sm" style="color: var(--text-secondary)">by { match.Author }</p>
+						}
+						<div class="mt-2 flex items-center gap-2">
+							<span class="text-xs px-2 py-1 rounded" style="background-color: var(--accent); color: var(--bg-primary);">
+								{ fmt.Sprintf("%.0f%% confidence", match.Confidence*100) }
+							</span>
+							<span class="text-xs" style="color: var(--text-secondary)">{ match.MatchMethod }</span>
+						</div>
+					</div>
+				</div>
+			</div>
+		}
+	}
+}
+
 templ UnlinkedBooks(user User, unlinkedBooks []UnlinkedBookData) {
 	<!DOCTYPE html>
 	<html lang="en">