feat(pwa): add Tier 1 support — installable app with manifest and icons

assets/icons/icon.svg

@@ -0,0 +1,18 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="512" height="512" viewBox="0 0 512 512">
+  <defs>
+    <linearGradient id="bg" x1="0" y1="0" x2="0" y2="1">
+      <stop offset="0" stop-color="#10243b"/>
+      <stop offset="1" stop-color="#081421"/>
+    </linearGradient>
+  </defs>
+  <rect width="512" height="512" fill="url(#bg)"/>
+  <!-- Header trophy logo (0 0 24 24 art), scaled to fill ~60% of the icon -->
+  <g transform="translate(40,48) scale(18)" fill="none" stroke="#d4af37" stroke-width="1.4" stroke-linecap="round" stroke-linejoin="round">
+    <circle cx="12" cy="5" r="1.8" fill="#d4af37" stroke="none"/>
+    <path d="M7 8h10v2.3a5 5 0 0 1-10 0V8z"/>
+    <path d="M7 8.4H4.6a2.6 2.6 0 0 0 2.4 3.4"/>
+    <path d="M17 8.4h2.4a2.6 2.6 0 0 1-2.4 3.4"/>
+    <path d="M12 15.3v2.2"/>
+    <rect x="9" y="18.3" width="6" height="1.6" rx="0.6" fill="#d4af37" stroke="none"/>
+  </g>
+</svg>