Fix book card button to render when url is set but amazonUrl is not; v1.1.38

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

src/AdminPage.tsx

@@ -3905,7 +3905,7 @@ async function handleAssetUpload(event: ChangeEvent<HTMLInputElement>) {
                       <input id={`book-amazon-label-${book.id}`} type="text" value={book.amazonLabel ?? ''} placeholder="View on Amazon" onChange={e => updateLink(book.id, 'amazonLabel', e.target.value)} />
                     </div>
                     <div className="admin-field">
-                      <label htmlFor={`book-url-${book.id}`}>Link URL <span className="admin-field-optional">(optional fallback)</span></label>
+                      <label htmlFor={`book-url-${book.id}`}>Link URL <span className="admin-field-optional">(used if no Amazon URL is set)</span></label>
                       <input id={`book-url-${book.id}`} type="url" value={book.url ?? ''} placeholder="https://..." onChange={e => updateLink(book.id, 'url', e.target.value)} />
                     </div>
                   </div>

src/App.tsx

@@ -1787,8 +1787,8 @@ function BooksSectionSection({ content }: { content: SiteContent }) {
               <div className="book-card-meta">
                 <span className="book-card-title">{book.label}</span>
                 {book.description && <p className="book-card-description">{book.description}</p>}
-                {book.amazonUrl && (
-                  <a href={book.amazonUrl} target="_blank" rel="noopener noreferrer" className="btn-primary book-card-btn">
+                {(book.amazonUrl || book.url) && (
+                  <a href={book.amazonUrl || book.url} target="_blank" rel="noopener noreferrer" className="btn-primary book-card-btn">
                     {book.amazonLabel || 'View on Amazon'}
                   </a>
                 )}