Add spatial audio and sound effect captions

index.html

@@ -252,6 +252,7 @@
             <section id="player-game-area">
                 <div class="level"><!-- level canvas and any overlays go here --></div>
                 <div class="player-overlay-message"></div>
+                <div class="player-overlay-captions"></div>
                 <div class="player-hint-wrapper">
                     <div class="player-hint"></div>
                     <svg class="player-hint-bg-icon svg-icon" viewBox="0 0 16 16"><use href="#svg-icon-hint"></use></svg>