feat(frontend): installable on the phone with its own icon, title and manifest, missing avatars are asked again later

frontend/static/manifest.webmanifest

@@ -0,0 +1,20 @@
+{
+  "name": "Beavergram",
+  "short_name": "Beavergram",
+  "start_url": "/app",
+  "scope": "/",
+  "display": "standalone",
+  "background_color": "#212121",
+  "theme_color": "#212121",
+  "icons": [
+    { "src": "/icon-192.png", "sizes": "192x192", "type": "image/png" },
+    { "src": "/icon-512.png", "sizes": "512x512", "type": "image/png" },
+    {
+      "src": "/icon-512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "maskable"
+    },
+    { "src": "/icon.svg", "sizes": "any", "type": "image/svg+xml" }
+  ]
+}