Improve accessibility for screen reader users

- Marked UI regions with ARIA landmarks
- Added text labels to icon-only buttons
- Added ARIA state semantics to track star buttons
- Added static alt text to cover art images

approot/main.xml

@@ -3,11 +3,11 @@
 
 <message id="Lms.main.template">
 	${navbar}
-	<div class="container">
+	<main class="container">
 		${contents}
 		${notifications class="toast-container Lms-notification-container p-3"}
 		${modal}
-	</div>
+	</main>
 	${player class="fixed-bottom bg-dark Lms-player"}
 </message>