chore: migrate to TypeScript

- Convert all .js files to .tsx/.ts
- Add types for data structures (MuseumRecord, Metrics, etc.)
- Add type declarations for react-chartjs-2
- Configure tsconfig with relaxed strictness for gradual adoption
- All components now use TypeScript

src/index.tsx

@@ -0,0 +1,13 @@
+import React from 'react';
+import ReactDOM from 'react-dom/client';
+import { LanguageProvider } from './contexts/LanguageContext';
+import App from './App';
+
+const root = ReactDOM.createRoot(document.getElementById('root'));
+root.render(
+  <React.StrictMode>
+    <LanguageProvider>
+      <App />
+    </LanguageProvider>
+  </React.StrictMode>
+);