Remove all highlights from panel tutorial steps, fix minimap z-index (#55, #57)

- Remove highlight entirely from Quiz Panel, Video Sidebar, and
  domain exploration steps (panels are already visually prominent)
- Lower minimap z-index in landscape mode so it stays behind video panel

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jeremymanning

index.html

@@ -889,7 +889,7 @@
             #minimap-container {
                 width: 160px; height: 120px;
                 bottom: 12px; left: 12px;
-                z-index: 10; /* Above quiz/video panel toggles */
+                z-index: 3; /* Below panels and toggles */
             }
             /* Quiz panel: right-side drawer in landscape */
             #quiz-panel.open { height: auto; max-height: 100%; }

src/ui/tutorial.js

@@ -36,7 +36,6 @@ const STEPS = [
   },
   {
     id: 2, title: 'The Quiz Panel',
-    highlight: '#quiz-toggle',
     arrowTarget: '#quiz-toggle',
     arrowSide: 'above',
     positionHint: 'quiz-final',
@@ -51,7 +50,6 @@ const STEPS = [
     id: 3, title: 'Video Sidebar', subSteps: [
       {
         title: 'Video Sidebar',
-        highlight: '#video-toggle',
         arrowTarget: '#video-toggle',
         arrowSide: 'above',
         positionHint: 'video-final',
@@ -61,7 +59,6 @@ const STEPS = [
       },
       {
         title: 'Video Sidebar',
-        highlight: '#video-toggle',
         positionHint: 'video-final',
         message: () => {
           const touch = 'ontouchstart' in window || navigator.maxTouchPoints > 0;