feat: copy code block button

static/js/copy-code.js

@@ -0,0 +1,27 @@
+// NOTE: Pelican's fenced_code puts language-* on <code>, not <pre>,
+// so we select the <code> elements and walk up to the <pre>.
+const codeBlocks = document.querySelectorAll('code[class*="language-"]');
+
+console.log("copy-code.js loaded, found:", codeBlocks.length);
+
+codeBlocks.forEach((code) => {
+  const pre = code.closest("pre");
+  if (!pre) return;
+
+  const button = document.createElement("button");
+  button.className = "copy-to-clipboard-button";
+  button.type = "button";
+  button.textContent = "Copy";
+
+  button.addEventListener("click", async () => {
+    try {
+      await navigator.clipboard.writeText(code.innerText);
+      button.textContent = "Copied";
+    } catch {
+      button.textContent = "Failed";
+    }
+    setTimeout(() => (button.textContent = "Copy"), 1500);
+  });
+
+  pre.appendChild(button);
+});