revert(web): drop the 32x32 PNG favicon fallback

The SVG media query alone fixes the dark-mode icon for every SVG-capable
browser (Chrome, Edge, Firefox, Safari 26+); the PNG only served Safari
versions before 26, which is a shrinking legacy audience not worth a second
asset, its manifest/link declarations, and the extra test surface. index.html
and the manifest are back to the single SVG icon.

apps/web/public/manifest.webmanifest

@@ -6,12 +6,6 @@
   "scope": "/",
   "display": "fullscreen",
   "icons": [
-    {
-      "src": "/favicon-32x32.png",
-      "sizes": "32x32",
-      "type": "image/png",
-      "purpose": "any"
-    },
     {
       "src": "/favicon.svg",
       "sizes": "any",