Capture every space press

Otherwise spacebar does not work if focus is on the sound input or a
bookmark link (in development). We will need to revise the approach if
we make any text input fields.

app/audio-player/contentscript.js

@@ -40,11 +40,13 @@ export default async function init() {
 	}
 
 	document.body.addEventListener('keydown', event => {
-		if (event.target !== document.body) return;
+		// Pressing spacebar triggers play/pause.
 		if (event.code === 'Space') {
 			playpause();
+			event.stopPropagation();
+			event.preventDefault();
 		}
-	});
+	}, { capture: true });
 
 	// Load the file
 	await playlist.load([{