fix(docs): hide sidebar placeholders on index pages

Use a data attribute on docs index containers so sidebar placeholders and panels can be hidden with CSS while preserving the existing layout column override.

src/routes/$.tsx

@@ -236,10 +236,8 @@ function Page() {
 
   const indexLayoutProps = data.isIndex
     ? {
-        sidebar: {
-          enabled: false,
-        },
         containerProps: {
+          'data-docs-index': true,
           style: {
             '--fd-sidebar-col': '0px',
           } as CSSProperties,

src/styles/app.css

@@ -62,3 +62,8 @@ body {
 [data-media-card] p {
   margin: 0 !important;
 }
+
+[data-docs-index] [data-sidebar-placeholder],
+[data-docs-index] [data-sidebar-panel] {
+  display: none;
+}