fix settings tabs by using inline style.display instead of CSS class toggling

The class-based is-active/display approach was unreliable due to CSS cascade
issues. Switching to direct style.display manipulation bypasses specificity
entirely. Also added cache-busting ?v=2 to style.css link.

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

app/templates/layout.html

@@ -7,7 +7,7 @@
   <link rel="icon" href="{{ url_for('static', filename='favicon.svg') }}" type="image/svg+xml">
   <link rel="icon" href="{{ url_for('static', filename='favicon.ico') }}" sizes="any">
   <link rel="apple-touch-icon" href="{{ url_for('static', filename='apple-touch-icon.png') }}">
-  <link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}">
+  <link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}?v=2">
   {% block head %}{% endblock %}
 </head>
 <body{% block body_attrs %}{% endblock %}>