feat: PWA + full web app — service worker, routing, mobile responsive

frontend/public/icons/icon.svg

@@ -0,0 +1,11 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
+  <rect width="512" height="512" rx="100" fill="#090910"/>
+  <polygon points="290,60 150,280 240,280 222,452 370,220 272,220" fill="#6366f1"/>
+  <polygon points="290,60 150,280 240,280 222,452 370,220 272,220" fill="url(#g)" opacity="0.4"/>
+  <defs>
+    <linearGradient id="g" x1="0" y1="0" x2="1" y2="1">
+      <stop offset="0%" stop-color="#a78bfa"/>
+      <stop offset="100%" stop-color="#818cf8" stop-opacity="0"/>
+    </linearGradient>
+  </defs>
+</svg>