Add a friendly 502/503/504 page (nginx serves it directly, no backend needed)

nginx-502.html

@@ -0,0 +1,23 @@
+<!doctype html>
+<html lang="sk">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <meta http-equiv="refresh" content="5">
+  <title>Print server</title>
+  <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.8/dist/css/bootstrap.min.css" rel="stylesheet">
+  <link href="https://cdn.jsdelivr.net/npm/@mdi/font@7.4.47/css/materialdesignicons.min.css" rel="stylesheet">
+  <style>
+    body { background: #212529; color: #adb5bd; }
+    .mdi-printer-off { font-size: 4rem; color: #6c757d; }
+  </style>
+</head>
+<body class="d-flex align-items-center justify-content-center vh-100">
+  <div class="text-center">
+    <i class="mdi mdi-printer-off"></i>
+    <h1 class="mt-3">Tlačiareň spí</h1>
+    <p class="text-muted">Print server práve nabieha alebo sa reštartuje.<br>Stránka sa sama skúsi znova o chvíľu...</p>
+    <div class="spinner-border text-secondary mt-2" role="status"></div>
+  </div>
+</body>
+</html>