feat: add Progressive Web App (PWA) support with service worker registration, manifest, update notifications, and install prompts

frontend/icons/search-96x96.svg

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg width="96" height="96" viewBox="0 0 96 96" xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <linearGradient id="grad1" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#2563eb;stop-opacity:1" />
+      <stop offset="100%" style="stop-color:#1d4ed8;stop-opacity:1" />
+    </linearGradient>
+  </defs>
+  
+  <!-- Background -->
+  <rect width="96" height="96" rx="14.399999999999999" fill="url(#grad1)"/>
+  
+  <!-- Search icon -->
+  <g transform="translate(19.200000000000003, 19.200000000000003)">
+    <circle cx="24.0" cy="24.0" r="17.28" fill="none" stroke="white" stroke-width="4.800000000000001" opacity="0.95"/>
+    <line x1="36.480000000000004" y1="36.480000000000004" x2="48.0" y2="48.0" stroke="white" stroke-width="4.800000000000001" stroke-linecap="round" opacity="0.95"/>
+  </g>
+</svg>