Add API layer, Zustand store, markdown renderer, types

lib/markdown.ts

@@ -0,0 +1,11 @@
+import { marked } from 'marked';
+
+marked.setOptions({
+  breaks: true,
+  gfm: true,
+});
+
+export function renderMarkdown(text: string): string {
+  if (!text) return '';
+  return marked.parse(text) as string;
+}