Fix: Language switch takes effect immediately (React Context)

Replaced localStorage-only hook with React Context Provider.
Layout and page components now share the same state — switching
language in the dropdown instantly updates all text on screen
without requiring a page reload.

NativeLanguageProvider added to root layout.tsx.
useNativeLanguage() re-exported from Context for backward compat.

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

studio-v2/app/layout.tsx

@@ -6,6 +6,7 @@ import { AlertsProvider } from '@/lib/AlertsContext'
 import { AlertsB2BProvider } from '@/lib/AlertsB2BContext'
 import { MessagesProvider } from '@/lib/MessagesContext'
 import { ActivityProvider } from '@/lib/ActivityContext'
+import { NativeLanguageProvider } from '@/lib/NativeLanguageContext'
 
 export const metadata: Metadata = {
   title: 'BreakPilot Studio v2',
@@ -26,7 +27,9 @@ export default function RootLayout({
               <AlertsB2BProvider>
                 <MessagesProvider>
                   <ActivityProvider>
-                    {children}
+                    <NativeLanguageProvider>
+                      {children}
+                    </NativeLanguageProvider>
                   </ActivityProvider>
                 </MessagesProvider>
               </AlertsB2BProvider>