fix uptime showing undefined on dashboard

initialData for / route was missing uptimeHuman — only /health and /status
computed it. Add uptime calculation to the dashboard render path.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

health-server.js

@@ -2090,8 +2090,10 @@ const server = http.createServer((req, res) => {
   if (pathname === "/" || pathname === "") {
     void (async () => {
       const postiz = await checkPostizHealth();
+      const uptime = Math.floor((Date.now() - startTime) / 1000);
       const initialData = {
         postizRunning: postiz.status === "running",
+        uptimeHuman: formatUptime(uptime),
         keepalive: getKeepaliveStatus(),
         sync: readSyncStatus(),
       };