Add closing slide section with QR codes and styling enhancements

- Introduced a new closing slide section in index.html to thank the audience and provide QR codes for easy access to the repository and slides.
- Added corresponding CSS styles in custom.css to enhance the presentation of the closing slide elements, including layout and typography adjustments.
- Implemented QR code generation for the repository and slides using JavaScript for improved user engagement.

content/kubernetes-hell-to-heaven/css/custom.css

@@ -284,3 +284,70 @@
   color: var(--accent-cyan);
   font-weight: 600;
 }
+
+/* Slide de fin : remerciement, Q/R, QR codes */
+.reveal section.slide-fin h1 {
+  margin: 0 0 0.2em;
+  font-size: clamp(1.15em, 5vw, 1.45em);
+}
+
+.reveal section.slide-fin .slide-fin-thanks {
+  margin: 0 0 0.15em;
+  font-size: 0.52em;
+  line-height: 1.35;
+  color: var(--text-muted);
+}
+
+.reveal section.slide-fin .slide-fin-cta {
+  margin: 0 0 0.35em;
+  font-size: 0.72em;
+  font-weight: 600;
+  color: var(--accent-cyan);
+}
+
+.reveal section.slide-fin .slide-fin-hint {
+  margin: 0 auto 0.45em;
+  max-width: 28em;
+  font-size: 0.38em;
+  line-height: 1.4;
+  color: var(--text-subtle);
+}
+
+.reveal section.slide-fin .slide-fin-qr-grid {
+  display: flex;
+  flex-wrap: wrap;
+  justify-content: center;
+  align-items: flex-end;
+  gap: 0.85em 1.75em;
+  margin: 0.15em 0 0;
+}
+
+.reveal section.slide-fin .slide-fin-qr-block {
+  margin: 0;
+  padding: 0;
+  border: none;
+  text-align: center;
+}
+
+.reveal section.slide-fin .slide-fin-qr-block figcaption {
+  margin: 0 0 0.35em;
+  font-size: 0.36em;
+  font-weight: 600;
+  color: var(--text-muted);
+}
+
+.reveal section.slide-fin .qrcode-fin-wrap {
+  display: inline-block;
+  padding: 0.2em;
+  background: #fff;
+  border-radius: 8px;
+  line-height: 0;
+  box-shadow: 0 2px 12px rgba(0, 0, 0, 0.25);
+}
+
+.reveal section.slide-fin .qrcode-fin-wrap canvas,
+.reveal section.slide-fin .qrcode-fin-wrap img {
+  display: block;
+  width: 150px;
+  height: 150px;
+}