Initial commit: ElysiaJS backend + TanStack Start frontend + Traefik compose

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/routes/index.tsx

@@ -0,0 +1,47 @@
+import { createFileRoute } from "@tanstack/react-router";
+import { useEffect, useState } from "react";
+
+export const Route = createFileRoute("/")({
+  component: Home,
+});
+
+// Public URL of the backend, injected at build time via Vite.
+// Falls back to localhost for `vite dev`.
+const API_URL = import.meta.env.VITE_API_URL ?? "http://localhost:3000";
+
+type Hello = { message: string; timestamp: string };
+
+function Home() {
+  const [data, setData] = useState<Hello | null>(null);
+  const [error, setError] = useState<string | null>(null);
+
+  useEffect(() => {
+    fetch(`${API_URL}/api/hello`)
+      .then((r) => {
+        if (!r.ok) throw new Error(`HTTP ${r.status}`);
+        return r.json() as Promise<Hello>;
+      })
+      .then(setData)
+      .catch((e) => setError(String(e)));
+  }, []);
+
+  return (
+    <main style={{ fontFamily: "system-ui, sans-serif", padding: "2rem", maxWidth: 640, margin: "0 auto" }}>
+      <h1>test-app-stack</h1>
+      <p>TanStack Start frontend talking to an ElysiaJS (Bun) backend.</p>
+
+      <section style={{ marginTop: "1.5rem", padding: "1rem", border: "1px solid #ddd", borderRadius: 8 }}>
+        <h2 style={{ marginTop: 0 }}>Backend connection</h2>
+        <p><strong>API URL:</strong> <code>{API_URL}</code></p>
+        {error && <p style={{ color: "crimson" }}>❌ {error}</p>}
+        {!error && !data && <p>Connecting…</p>}
+        {data && (
+          <>
+            <p>✅ <strong>{data.message}</strong></p>
+            <p style={{ color: "#666", fontSize: "0.85rem" }}>at {data.timestamp}</p>
+          </>
+        )}
+      </section>
+    </main>
+  );
+}