feat: Phase 5.3 - PWA Offline Support with Workbox

- Add vite-plugin-pwa + workbox-window
- Configure PWA manifest with icons (SVG)
- Configure Workbox runtime caching:
  - API routes: NetworkFirst (10s timeout, 100 entries, 24h)
  - Media files: CacheFirst (50 entries, 7 days)
  - Pages: NetworkFirst (10s timeout, 50 entries, 24h)
- Register service worker in app.js with update notification
- Generate icons (SVG) for all sizes

Tests: 101 passing (319 assertions)

public/icons/icon-128x128.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="128" height="128" viewBox="0 0 100 100">
+  <rect width="100" height="100" rx="20" fill="#2563eb"/>
+  <text x="50" y="62" font-family="Arial, sans-serif" font-size="50" font-weight="bold" fill="white" text-anchor="middle">CP</text>
+</svg>

public/icons/icon-144x144.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="144" height="144" viewBox="0 0 100 100">
+  <rect width="100" height="100" rx="20" fill="#2563eb"/>
+  <text x="50" y="62" font-family="Arial, sans-serif" font-size="50" font-weight="bold" fill="white" text-anchor="middle">CP</text>
+</svg>

public/icons/icon-152x152.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="152" height="152" viewBox="0 0 100 100">
+  <rect width="100" height="100" rx="20" fill="#2563eb"/>
+  <text x="50" y="62" font-family="Arial, sans-serif" font-size="50" font-weight="bold" fill="white" text-anchor="middle">CP</text>
+</svg>

public/icons/icon-192x192.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="192" height="192" viewBox="0 0 100 100">
+  <rect width="100" height="100" rx="20" fill="#2563eb"/>
+  <text x="50" y="62" font-family="Arial, sans-serif" font-size="50" font-weight="bold" fill="white" text-anchor="middle">CP</text>
+</svg>

public/icons/icon-384x384.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="384" height="384" viewBox="0 0 100 100">
+  <rect width="100" height="100" rx="20" fill="#2563eb"/>
+  <text x="50" y="62" font-family="Arial, sans-serif" font-size="50" font-weight="bold" fill="white" text-anchor="middle">CP</text>
+</svg>

public/icons/icon-512x512.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="512" height="512" viewBox="0 0 100 100">
+  <rect width="100" height="100" rx="20" fill="#2563eb"/>
+  <text x="50" y="62" font-family="Arial, sans-serif" font-size="50" font-weight="bold" fill="white" text-anchor="middle">CP</text>
+</svg>

public/icons/icon-72x72.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="72" height="72" viewBox="0 0 100 100">
+  <rect width="100" height="100" rx="20" fill="#2563eb"/>
+  <text x="50" y="62" font-family="Arial, sans-serif" font-size="50" font-weight="bold" fill="white" text-anchor="middle">CP</text>
+</svg>

public/icons/icon-96x96.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="96" height="96" viewBox="0 0 100 100">
+  <rect width="100" height="100" rx="20" fill="#2563eb"/>
+  <text x="50" y="62" font-family="Arial, sans-serif" font-size="50" font-weight="bold" fill="white" text-anchor="middle">CP</text>
+</svg>