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

Extract the duplicated `product !== null && product !== 'platform'` check
into `activePage.hasProductBar` computed once in the layout context,
replacing three identical copies in Layout, LeftSidebar, and RightSidebar.

Simplify useShowLanguageSelector double negation (!every(!includes)) to
the equivalent some(includes).

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

Author: m-hulbert

src/components/Layout/hooks/useShowLanguageSelector.ts

@@ -10,8 +10,8 @@ export const useShowLanguageSelector = () => {
     () =>
       activePage.isDualLanguage ||
       (activePage.languages.length > 0 &&
-        !activePage.languages.every(
-          (language) => !Object.keys(languageData[activePage.product as ProductKey] ?? {}).includes(language),
+        activePage.languages.some((language) =>
+          Object.keys(languageData[activePage.product as ProductKey] ?? {}).includes(language),
         )),
     [activePage.languages, activePage.product, activePage.isDualLanguage],
   );

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]);