feat: add proper favicon set from RealFaviconGenerator

Replace inline emoji favicon with full cross-platform favicon support
including SVG, PNG, ICO, Apple touch icon, and PWA manifest icons.

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

static/site.webmanifest

@@ -0,0 +1,21 @@
+{
+  "name": "Crumbs by Bretzel",
+  "short_name": "Crumbs",
+  "icons": [
+    {
+      "src": "/web-app-manifest-192x192.png",
+      "sizes": "192x192",
+      "type": "image/png",
+      "purpose": "maskable"
+    },
+    {
+      "src": "/web-app-manifest-512x512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "maskable"
+    }
+  ],
+  "theme_color": "#f9f4ea",
+  "background_color": "#f9f4ea",
+  "display": "standalone"
+}