added api logic, vitest, minimal testing ui

web/src/pages/HealthPage.tsx

@@ -0,0 +1,18 @@
+import { useQuery } from "@tanstack/react-query";
+import { api } from "../api/client";
+
+export default function HealthPage() {
+  const app = useQuery({ queryKey: ["health"], queryFn: () => api.get<{ok:true}>("/health") });
+  const db  = useQuery({ queryKey: ["health","db"], queryFn: () => api.get<{ok:true; nowISO:string; latencyMs:number}>("/health/db") });
+
+  return (
+    <div className="card max-w-lg">
+      <h2 className="section-title">Health</h2>
+      <ul className="stack">
+        <li>API: {app.isLoading ? "…" : app.data?.ok ? "OK" : "Down"}</li>
+        <li>DB: {db.isLoading ? "…" : db.data?.ok ? `OK (${db.data.latencyMs} ms)` : "Down"}</li>
+        <li>Server Time: {db.data?.nowISO ? new Date(db.data.nowISO).toLocaleString() : "…"}</li>
+      </ul>
+    </div>
+  );
+}