Fix home screen icon not displaying on Firefox for Android

Add a 48x48 icon (preferred by Firefox Android for home screen shortcuts)
and set explicit purpose: "any" on non-maskable icons, which Firefox
Android requires to properly select an icon for the home screen.

https://claude.ai/code/session_01L8ZJf9dRQM9bHU84USeRrE

Author: claude

public/icons/icon-48.png

@@ -7,15 +7,23 @@
   "theme_color": "#8B2252",
   "background_color": "#ffffff",
   "icons": [
+    {
+      "src": "/icons/icon-48.png",
+      "sizes": "48x48",
+      "type": "image/png",
+      "purpose": "any"
+    },
     {
       "src": "/icons/icon-192.png",
       "sizes": "192x192",
-      "type": "image/png"
+      "type": "image/png",
+      "purpose": "any"
     },
     {
       "src": "/icons/icon-512.png",
       "sizes": "512x512",
-      "type": "image/png"
+      "type": "image/png",
+      "purpose": "any"
     },
     {
       "src": "/icons/icon-maskable-512.png",