fix: close orphaned button tags in index.html HUD

Remove orphan <button> for atlas-toggle-btn (line 155) that was opened
but never closed and had no content. Add missing </button> for
soul-toggle-btn and mode-toggle-btn. Fixes broken HTML nesting.

Closes #1336

index.html

@@ -152,10 +152,10 @@
 
   <!-- Top Right: Agent Log, Atlas & SOUL Toggle -->
   <div class="hud-top-right">
-    <button id="atlas-toggle-btn" class="hud-icon-btn" title="World Directory">
     <button id="soul-toggle-btn" class="hud-icon-btn" title="Timmy's SOUL">
       <span class="hud-icon">✦</span>
       <span class="hud-btn-label">SOUL</span>
+    </button>
     <button id="mode-toggle-btn" class="hud-icon-btn mode-toggle" title="Toggle Mode">
       <span class="hud-icon">👁</span>
       <span class="hud-btn-label" id="mode-label">VISITOR</span>