docs: Preserve markdown when copying prompt blocks

Add prompt-copy.js that intercepts sphinx-copybutton on prompt
admonitions and reconstructs inline markdown from the DOM. Wraps
<code> elements in backticks so copied text preserves formatting
like `make test` instead of plain "make test".

Author: tony

docs/_static/js/prompt-copy.js

@@ -0,0 +1,63 @@
+/**
+ * Markdown-preserving copy for prompt blocks.
+ *
+ * sphinx-copybutton uses innerText which strips HTML. This script
+ * intercepts copy on .admonition.prompt buttons and reconstructs
+ * inline markdown (backtick-wrapping <code> elements) before copying.
+ */
+(function () {
+  function toMarkdown(el) {
+    var text = "";
+    for (var i = 0; i < el.childNodes.length; i++) {
+      var node = el.childNodes[i];
+      if (node.nodeType === Node.TEXT_NODE) {
+        text += node.textContent;
+      } else if (node.nodeType === Node.ELEMENT_NODE) {
+        if (node.tagName === "CODE") {
+          text += "`" + node.textContent + "`";
+        } else {
+          text += toMarkdown(node);
+        }
+      }
+    }
+    return text;
+  }
+
+  function init() {
+    var buttons = document.querySelectorAll(
+      "div.admonition.prompt button.copybtn"
+    );
+    buttons.forEach(function (btn) {
+      btn.addEventListener(
+        "click",
+        function (e) {
+          e.stopImmediatePropagation();
+          e.preventDefault();
+
+          var targetId = btn.getAttribute("data-clipboard-target");
+          var target = document.querySelector(targetId);
+          if (!target) return;
+
+          var markdown = toMarkdown(target);
+          navigator.clipboard.writeText(markdown).then(function () {
+            btn.setAttribute("data-tooltip", "Copied!");
+            btn.classList.add("success");
+            setTimeout(function () {
+              btn.setAttribute("data-tooltip", "Copy");
+              btn.classList.remove("success");
+            }, 2000);
+          });
+        },
+        true
+      );
+    });
+  }
+
+  if (document.readyState === "loading") {
+    document.addEventListener("DOMContentLoaded", function () {
+      setTimeout(init, 100);
+    });
+  } else {
+    setTimeout(init, 100);
+  }
+})();

docs/conf.py

@@ -291,4 +291,5 @@ def remove_tabs_js(app: Sphinx, exc: Exception) -> None:
 def setup(app: Sphinx) -> None:
     """Configure Sphinx app hooks."""
     app.add_js_file("js/spa-nav.js", loading_method="defer")
+    app.add_js_file("js/prompt-copy.js", loading_method="defer")
     app.connect("build-finished", remove_tabs_js)