feat(shell-docs): hide sidebar Quickstart entry until a framework is active

The root /quickstart page is a routing shim — it has no real content,
just a pointer to the per-framework quickstarts. Showing it in the
sidebar on / leads users into a dead-end click ("This page is a
routing shim..."). Hide the entry until a framework is active in the
URL or stored in localStorage; once either is set, SidebarLink prepends
it and the click lands on real per-framework content.

Author: samjulien

showcase/shell-docs/src/app/[[...slug]]/page.tsx

@@ -148,6 +148,7 @@ function OverviewNavItem({
       <div style={{ paddingLeft: `${indent}px` }}>
         <SidebarLink
           slug={node.slug}
+          hideWhenUnscoped={node.slug === "quickstart"}
           className="block py-[5px] text-[13px] text-[var(--text-muted)] hover:text-[var(--text-secondary)] transition-colors"
         >
           {node.title}

showcase/shell-docs/src/components/docs-page-view.tsx

@@ -140,6 +140,7 @@ export async function DocsPageView({
             scope={scope}
             fallbackHref={`${slugHrefPrefix}/${node.slug}`}
             active={isActive}
+            hideWhenUnscoped={node.slug === "quickstart"}
             className={`block py-[5px] text-[13px] transition-colors ${
               isActive
                 ? "text-[var(--accent)] font-medium"

showcase/shell-docs/src/components/sidebar-link.tsx

@@ -34,6 +34,14 @@ export interface SidebarLinkProps {
    * interface for call-site compatibility.
    */
   fallbackHref?: string;
+  /**
+   * When true, the link does not render unless a framework is active
+   * (URL-scoped) or stored in localStorage. Used for sidebar entries
+   * whose root MDX is a routing shim — e.g. Quickstart, whose real
+   * content lives per-framework. Without this, the entry shows on `/`
+   * but clicks land on the shim page.
+   */
+  hideWhenUnscoped?: boolean;
 }
 
 export function SidebarLink({
@@ -43,6 +51,7 @@ export function SidebarLink({
   active,
   scope: _scope,
   fallbackHref: _fallbackHref,
+  hideWhenUnscoped,
 }: SidebarLinkProps) {
   const { framework, storedFramework } = useFramework();
 
@@ -52,6 +61,7 @@ export function SidebarLink({
   // avoiding the visible RouterPivot redirect that would otherwise flicker
   // in the URL bar.
   const activeFramework = framework ?? storedFramework;
+  if (hideWhenUnscoped && !activeFramework) return null;
   const href = activeFramework ? `/${activeFramework}/${slug}` : `/${slug}`;
 
   return (