Add server-side health checks for service online status

- update-health.js: pings every service URL from script.js (single
  source of truth) in parallel every minute via cron and writes
  health.json; any HTTP response below 500 counts as online, 5xx as
  error, timeouts/DNS failures as offline; TLS validity ignored
- Card badges now show real state instead of a static Online label:
  grey Checking, green Online (with latency tooltip), amber Error
  (HTTP code), red Offline (reason); refreshed every 30 s
- Entrypoint runs a first sweep at boot; nginx serves /health.json
  with no-cache; README documents the behavior

script.js

@@ -424,7 +424,10 @@ function cardTemplate(s, idx) {
              style="--cat:${meta.color}; animation-delay:${Math.min(idx * 35, 400)}ms">
       <div class="card-head">
         <div class="card-icon" aria-hidden="true">${s.icon || "🔗"}</div>
-        <span class="status"><span class="dot"></span>Online</span>
+        <span class="status" data-status-url="${escapeHtml(s.url)}">
+          <span class="dot" aria-hidden="true"></span>
+          <span class="status-text">Checking…</span>
+        </span>
       </div>
       <div class="card-body">
         <span class="card-cat">${escapeHtml(meta.label)}</span>
@@ -555,6 +558,51 @@ function bindOpenWebUIChat() {
   });
 }
 
+// ---------------------------------------------------------------------------
+// Service health badges (server-side checks via health.json)
+// ---------------------------------------------------------------------------
+
+function applyHealth(health) {
+  const services = health?.services || {};
+  document.querySelectorAll(".status[data-status-url]").forEach((badge) => {
+    const url = badge.getAttribute("data-status-url");
+    const h = services[url];
+    const text = badge.querySelector(".status-text");
+    if (!text) return;
+
+    if (!h) {
+      badge.className = "status unknown";
+      text.textContent = "Unknown";
+      badge.title = "No health data yet";
+      return;
+    }
+
+    if (h.status === "online") {
+      badge.className = "status online";
+      text.textContent = "Online";
+      badge.title = h.latencyMs != null ? `${h.latencyMs} ms` : "";
+    } else if (h.status === "error") {
+      badge.className = "status error";
+      text.textContent = "Error";
+      badge.title = `HTTP ${h.code}`;
+    } else {
+      badge.className = "status offline";
+      text.textContent = "Offline";
+      badge.title = h.error || "Unreachable";
+    }
+  });
+}
+
+async function loadHealth() {
+  try {
+    const res = await fetch("health.json", { cache: "no-store" });
+    if (!res.ok) throw new Error(`HTTP ${res.status}`);
+    applyHealth(await res.json());
+  } catch {
+    // keep the current badges; the next poll will retry
+  }
+}
+
 // ---------------------------------------------------------------------------
 // Search / filter
 // ---------------------------------------------------------------------------
@@ -614,3 +662,5 @@ loadGpuStats();
 setInterval(loadGpuStats, 5000); // live GPU stats every 5 s
 loadOllamaStats();
 setInterval(loadOllamaStats, 5000); // live Ollama loaded models every 5 s
+loadHealth();
+setInterval(loadHealth, 30000); // service health badges every 30 s