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>
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