Fix markdown code block syntax highlighting

Marked v15 removed the highlight option from setOptions.
Use marked.use() with a custom renderer instead.

.pi/hooks/status-demo.ts

@@ -0,0 +1,11 @@
+import type { HookAPI } from "@mariozechner/pi-coding-agent";
+
+export default function (pi: HookAPI) {
+	pi.on("turn_start", async (_event, ctx) => {
+		ctx.ui.setStatus("demo", "🔄 Thinking...");
+	});
+
+	pi.on("turn_end", async (_event, ctx) => {
+		ctx.ui.setStatus("demo", "✓ Ready");
+	});
+}