Add syntax highlighting and light/dark themes to twui CodeBlock

- Highlight string children with refractor (Prism) when `language` is
  set, rendered as React token spans; add ini/bash/json/yaml/ts support
- Add `theme` prop (auto | light | dark); auto follows the `.dark` class.
  Palettes are `--twui-code-*` CSS variables (GitHub Light/Dark, all
  tokens WCAG AA) so custom themes need no component changes
- Fix layout: real padding, singleBlock copy button no longer covers
  the code, clipped rounded corners, wrapperProps.style honoured,
  long tokens wrap
- MDX helpers take `codeTheme` and no longer force a black background
- Highlight WireGuard config blocks as ini

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/components/twui/(partials)/CodeBlockHastNode.tsx

@@ -0,0 +1,32 @@
+import type { RootContent } from "hast";
+
+type Props = {
+    node: RootContent;
+};
+
+/**
+ * # Render one node of a refractor hast tree
+ */
+export default function CodeBlockHastNode({ node }: Props) {
+    if (node.type === "text") {
+        return node.value;
+    }
+
+    if (node.type !== "element") {
+        return null;
+    }
+
+    const className = node.properties?.className;
+
+    return (
+        <span
+            className={
+                Array.isArray(className) ? className.join(" ") : undefined
+            }
+        >
+            {node.children.map((child, index) => (
+                <CodeBlockHastNode key={index} node={child} />
+            ))}
+        </span>
+    );
+}