chore(audio): tuck audio diagnostics (status + native player) under Dev Mode

The 'no sound' debugging is resolved (stale-server resilience). Move the audio
status readout + native test player into the Dev Mode panel — kept for future
'can't hear' debugging, out of the installation UI. 7 E2E pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

simulator/static/index.html

@@ -40,15 +40,6 @@
           <span class="dev-switch-track"><span class="dev-switch-thumb"></span></span>
           <span class="dev-switch-label">Audio</span>
         </label>
-        <div id="audio-status" class="audio-status">audio: off</div>
-      </fieldset>
-
-      <fieldset>
-        <legend>Audio check (diagnostic)</legend>
-        <p class="hint">Press play below to test the soundtrack file directly in the
-          browser's own player — this bypasses all app code. If you hear it here but
-          not from the Audio toggle, the file is fine and it's a code/autoplay issue.</p>
-        <audio id="aud-test" controls preload="auto" src="/media/audio/cosmos/pillars.loop.mp3" style="width:100%"></audio>
       </fieldset>
 
       <fieldset>
@@ -75,6 +66,15 @@
       </label>
 
       <div id="dev-panel" class="dev-panel hidden">
+        <fieldset>
+          <legend>Audio diagnostics</legend>
+          <div id="audio-status" class="audio-status">audio: off</div>
+          <p class="hint">Native player — tests the soundtrack file directly (bypasses
+            all app code). If it plays here but the Audio toggle is silent, it's a
+            code/autoplay issue, not the file.</p>
+          <audio id="aud-test" controls preload="auto" src="/media/audio/cosmos/pillars.loop.mp3" style="width:100%"></audio>
+        </fieldset>
+
         <fieldset>
           <legend>Pool — pick a clip</legend>
           <select id="pool-select" aria-label="Choose a clip from this altitude's pool"></select>