feat: Add PWA support and CORS configuration

- Configure VitePWA with manifest, icons and service worker
- Add PwaInstallBanner component for install prompt in header
- Enable CORS for z590.interno.com access
- Use dynamic hostname for terminal WebSocket connection
- Add generate-icons script with sharp for PWA icons
- Fix theme-color to match header background

frontend/public/icons/icon.svg

@@ -0,0 +1,18 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
+  <defs>
+    <linearGradient id="bg" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#667eea"/>
+      <stop offset="100%" style="stop-color:#764ba2"/>
+    </linearGradient>
+    <linearGradient id="accent" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#4facfe"/>
+      <stop offset="100%" style="stop-color:#00f2fe"/>
+    </linearGradient>
+  </defs>
+  <rect width="512" height="512" rx="96" fill="url(#bg)"/>
+  <circle cx="256" cy="200" r="80" fill="none" stroke="white" stroke-width="16" opacity="0.9"/>
+  <circle cx="256" cy="200" r="40" fill="url(#accent)"/>
+  <rect x="156" y="320" width="200" height="24" rx="12" fill="white" opacity="0.8"/>
+  <rect x="186" y="360" width="140" height="16" rx="8" fill="white" opacity="0.5"/>
+  <rect x="206" y="392" width="100" height="16" rx="8" fill="white" opacity="0.3"/>
+</svg>