refactor(nav): extract hasProductBar to layout context and simplify hooks

Extract the duplicated product bar visibility check into
activePage.hasProductBar, computed once in the layout context. Simplify
useShowLanguageSelector double negation to the equivalent some().

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: m-hulbert

src/components/Layout/utils/nav.ts

@@ -20,6 +20,7 @@ export type ActivePage = {
   clientLanguages?: LanguageKey[];
   agentLanguages?: LanguageKey[];
   isDualLanguage?: boolean;
+  hasProductBar: boolean;
 };
 
 /**

src/contexts/layout-context.tsx

@@ -40,6 +40,7 @@ const LayoutContext = createContext<{
     clientLanguages: [],
     agentLanguages: [],
     isDualLanguage: false,
+    hasProductBar: false,
   },
 });
 
@@ -117,18 +118,21 @@ export const LayoutProvider: React.FC<PropsWithChildren<{ pageContext: PageConte
     const clientLanguage = isDualLanguage ? determineClientLanguage(location.search, clientLanguages) : undefined;
     const agentLanguage = isDualLanguage ? determineAgentLanguage(location.search, agentLanguages) : undefined;
 
+    const product = activePageData?.product ?? null;
+
     return {
       tree: activePageData?.tree ?? [],
       page: activePageData?.page ?? { name: '', link: '' },
       languages,
       language: languages.includes(language) ? language : null,
-      product: activePageData?.product ?? null,
+      product,
       template: 'mdx' as PageTemplate,
       clientLanguage,
       agentLanguage,
       clientLanguages,
       agentLanguages,
       isDualLanguage,
+      hasProductBar: product !== null && product !== 'platform',
     };
   }, [location.pathname, location.search, pageContext?.languages]);