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

frontend/icons/icon-152x152.svg

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg width="152" height="152" viewBox="0 0 152 152" 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="152" height="152" rx="22.8" fill="url(#grad1)"/>
+  
+  <!-- Book icon -->
+  <g transform="translate(38.0, 30.400000000000002)">
+    <!-- Book cover -->
+    <rect x="0" y="0" width="76.0" height="91.2" rx="3.04" fill="white" opacity="0.95"/>
+    
+    <!-- Book spine -->
+    <rect x="7.6000000000000005" y="0" width="3.04" height="91.2" fill="#1a1a1a" opacity="0.2"/>
+    
+    <!-- Book pages lines -->
+    <line x1="15.200000000000001" y1="22.8" x2="68.4" y2="22.8" stroke="#1a1a1a" stroke-width="1.52" opacity="0.3"/>
+    <line x1="15.200000000000001" y1="38.0" x2="68.4" y2="38.0" stroke="#1a1a1a" stroke-width="1.52" opacity="0.3"/>
+    <line x1="15.200000000000001" y1="53.199999999999996" x2="68.4" y2="53.199999999999996" stroke="#1a1a1a" stroke-width="1.52" opacity="0.3"/>
+    <line x1="15.200000000000001" y1="68.4" x2="53.199999999999996" y2="68.4" stroke="#1a1a1a" stroke-width="1.52" opacity="0.3"/>
+  </g>
+</svg>