Sync slides 3-4 from master

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

index.html

@@ -70,6 +70,12 @@
   </section>
 
   <!-- ─── SLIDE 3 ──────────────────────────────────────────────────── -->
+  <section>
+    <h2>"It works on my server."</h2>
+    <p><em>Or: why doesn't it work here, when it works everywhere else?</em></p>
+  </section>
+
+  <!-- ─── SLIDE 4 ──────────────────────────────────────────────────── -->
   <section>
     <h2>You have a server. It works.</h2>
     <p><em>Great.</em></p>