add basic web app manifest, maybe this is enough to 'install' as standalone?

dlibrary/static/manifest.json

@@ -0,0 +1,20 @@
+{
+    "name": "DLibrary",
+    "start_url": "../index.html",
+    "display": "standalone",
+    "orientation": "any",
+    "theme_color": "#111",
+    "background_color": "#111",
+    "icons": [
+        {
+            "src": "icons/app/icon-192.png",
+            "sizes": "192x192",
+            "type": "image/png"
+        },
+        {
+            "src": "icons/app/icon-512.png",
+            "sizes": "512x512",
+            "type": "image/png"
+        }
+    ]
+}

dlibrary/templates/base.html

@@ -6,6 +6,7 @@
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <meta name="color-scheme" content="dark">
     <title>{% block title %}{% if title %}{{ title }} - {% else %}{% endif %}DLibrary{% endblock %}</title>
+    <link rel="manifest" href="{{ root() }}/static/manifest.json">
     <link rel="stylesheet" type="text/css" href="{{ root() }}/static/dlibrary.css">
     {% block head %}{% endblock %}
   </head>