Add OpenCS2 favicon set (32/192/512 PNG, transparent corners)

- Process favicon.png: corner-floodfill the pure-black bg to alpha (interior
dark navy preserved), trim, render at 32/192/512 with Lanczos, oxipng -o max
- Total assets: 1.7K + 25K + 179K (vs 1MB original)
- Layout head: rel=icon for 32/192/512 + apple-touch-icon at 192
- Drop the old emoji-based favicon.svg (and src/lib/assets/)

src/routes/+layout.svelte

@@ -1,7 +1,6 @@
 <script lang="ts">
 	import { page } from '$app/state';
 	import './layout.css';
-	import favicon from '$lib/assets/favicon.svg';
 	import { site } from '$lib/site';
 	import { ModeWatcher } from 'mode-watcher';
 	import { Toaster } from '$lib/components/ui/sonner';
@@ -17,8 +16,10 @@
 
 <svelte:head>
 	<title>{site.name}</title>
-	<link rel="icon" type="image/svg+xml" href={favicon} />
-	<link rel="apple-touch-icon" href={favicon} />
+	<link rel="icon" type="image/png" sizes="32x32" href="/favicon-32.png" />
+	<link rel="icon" type="image/png" sizes="192x192" href="/favicon-192.png" />
+	<link rel="icon" type="image/png" sizes="512x512" href="/favicon-512.png" />
+	<link rel="apple-touch-icon" sizes="192x192" href="/favicon-192.png" />
 	<link rel="canonical" href={canonicalUrl} />
 	<link rel="author" href={site.websiteUrl} />
 	<link rel="me" href={site.githubUrl} />