web: SVG favicon (Greek lowercase mu) with light/dark adaptive fill

Use the Greek lowercase mu glyph as the app's favicon. The SVG
carries a `prefers-color-scheme` media query that flips the path
fill between near-black (light mode) and near-white (dark mode),
so it stays legible against any tab-bar background without an
extra browser hint.

Linked before the existing PNG so browsers that support SVG
favicons (Chrome 80+, Firefox 41+, Safari 9+) pick it up; the PNG
remains as a fallback. `apple-touch-icon` keeps the PNG since iOS
home-screen icons can't be SVG.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/app.html

@@ -4,6 +4,11 @@
 		<meta charset="utf-8" />
 		<meta name="viewport" content="width=device-width, initial-scale=1" />
 		<meta name="text-scale" content="scale" />
+		<!-- SVG favicon adapts to light/dark via `prefers-color-scheme`
+		     inside the file itself; PNG remains as a fallback for browsers
+		     that don't support SVG icons. Apple touch icon stays PNG
+		     since iOS home-screen icons can't be SVG. -->
+		<link rel="icon" type="image/svg+xml" href="/favicon.svg" />
 		<link rel="icon" type="image/png" href="/favicon.png" />
 		<link rel="apple-touch-icon" href="/favicon.png" />
 		%sveltekit.head%