fix(web): favicon missing on the audiobook listening page

audio_reader.templ's <head> was the only page head without the
favicon link — the tab icon vanished the moment you opened a
listener. Standard <link rel=icon> added, matching every sibling
page.

templates/audio_reader.templ

@@ -17,6 +17,7 @@ templ AudioReader(user User, metadata ReaderMetadata) {
 			<meta charset="utf-8"/>
 			<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
 			<link href="/static/style.css" rel="stylesheet"/>
+			<link rel="icon" type="image/svg+xml" href="/static/favicon.svg"/>
 			<script type="module" src="/static/main.js"></script>
 			<style>
 				/* Layered scrubber (plan §1): the native range stays for