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

frontend/icons/icon-192x192.svg

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg width="192" height="192" viewBox="0 0 192 192" 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="192" height="192" rx="28.799999999999997" fill="url(#grad1)"/>
+  
+  <!-- Book icon -->
+  <g transform="translate(48.0, 38.400000000000006)">
+    <!-- Book cover -->
+    <rect x="0" y="0" width="96.0" height="115.19999999999999" rx="3.84" fill="white" opacity="0.95"/>
+    
+    <!-- Book spine -->
+    <rect x="9.600000000000001" y="0" width="3.84" height="115.19999999999999" fill="#1a1a1a" opacity="0.2"/>
+    
+    <!-- Book pages lines -->
+    <line x1="19.200000000000003" y1="28.799999999999997" x2="86.4" y2="28.799999999999997" stroke="#1a1a1a" stroke-width="1.92" opacity="0.3"/>
+    <line x1="19.200000000000003" y1="48.0" x2="86.4" y2="48.0" stroke="#1a1a1a" stroke-width="1.92" opacity="0.3"/>
+    <line x1="19.200000000000003" y1="67.19999999999999" x2="86.4" y2="67.19999999999999" stroke="#1a1a1a" stroke-width="1.92" opacity="0.3"/>
+    <line x1="19.200000000000003" y1="86.4" x2="67.19999999999999" y2="86.4" stroke="#1a1a1a" stroke-width="1.92" opacity="0.3"/>
+  </g>
+</svg>