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

frontend/static/icon.svg

@@ -0,0 +1,18 @@
+<svg viewBox="0 0 512 512" xmlns="http://www.w3.org/2000/svg">
+  <title>Beavergram</title>
+  <defs>
+    <linearGradient id="bg" x1="0" x2="0" y1="0" y2="1">
+      <stop offset="0" stop-color="#4fa3f3" />
+      <stop offset="1" stop-color="#2b7fdc" />
+    </linearGradient>
+  </defs>
+  <rect fill="url(#bg)" height="512" rx="112" width="512" />
+  <path d="M112 222 396 106 224 252Z" fill="#fff" />
+  <path d="M396 106 224 252 330 300Z" fill="#fff" fill-opacity=".86" />
+  <path d="M224 252 230 314 266 270Z" fill="#fff" fill-opacity=".7" />
+  <path
+    d="M128 344h256v28a36 36 0 0 1-36 36H164a36 36 0 0 1-36-36Z"
+    fill="#fff"
+  />
+  <rect fill="#3a8be6" height="14" rx="7" width="80" x="216" y="362" />
+</svg>