Add admin-editable QR code image to homepage share section

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

src/App.tsx

@@ -1446,7 +1446,7 @@ function LandingPage({ content }: { content: SiteContent }) {
             <p className="share-p">{content.shareP || 'Scan the QR code or text the show link to a friend who needs encouragement today.'}</p>
             <ShareShowButton />
           </div>
-          <img src="/images/qr-code.jpg" alt="QR code to share the show" className="share-qr" />
+          <img src={content.shareQrImageUrl || '/images/qr-code.jpg'} alt="QR code to share the show" className="share-qr" />
         </div>
       </section>