feat: add favicon and PWA icons (hexagon V, purple brand)

- favicon.ico (16+32+48px)
- favicon-16/32/48.png
- apple-touch-icon.png (180px)
- icon-192/512.png for PWA manifest
- site.webmanifest for installable PWA

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/site.webmanifest

@@ -0,0 +1,13 @@
+{
+  "name": "VanityOnTour Status",
+  "short_name": "VoT Status",
+  "description": "Status aller VanityOnTour Dienste, Domains und der iOS App",
+  "start_url": "/",
+  "display": "standalone",
+  "background_color": "#0f0f13",
+  "theme_color": "#7c3aed",
+  "icons": [
+    { "src": "/icon-192.png", "sizes": "192x192", "type": "image/png" },
+    { "src": "/icon-512.png", "sizes": "512x512", "type": "image/png", "purpose": "any maskable" }
+  ]
+}