fix(audio-reader): valid doctype — page loaded in quirks mode

audio_reader.templ was the only template emitting <!DOCTYPE html/>
(trailing slash is a parse error), which put the audio player page in
quirks mode — document.compatMode was BackCompat while every other
page is CSS1Compat. Quirks layout rules are a standing hazard for the
player's h-screen/flex page even where it happens to render. Drop the
slash.

templates/audio_reader.templ

@@ -10,7 +10,7 @@ package templates
 import "fmt"
 
 templ AudioReader(user User, metadata ReaderMetadata) {
-	<!DOCTYPE html/>
+	<!DOCTYPE html>
 	<html lang="en">
 		<head>
 			<title>{ "Listening · " + metadata.Title } · Bookhoard</title>