Add project files

react-project/src/App.js

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+import React, { useState } from 'react';
+import './App.css';
+
+function App() {
+  const [count, setCount] = useState(0);
+  
+  return (
+    <div className="App">
+      <header className="App-header">
+        <h1>React Docker Demo</h1>
+        <p>Diese App läuft in einem Docker-Container</p>
+        
+        <div className="counter">
+          <p>Du hast den Button {count} mal geklickt</p>
+          <button onClick={() => setCount(count + 1)}>
+            Klick mich!
+          </button>
+        </div>
+        
+        <p className="info">
+          Build-Zeit: {process.env.REACT_APP_BUILD_TIME || 'Unbekannt'}
+        </p>
+      </header>
+    </div>
+  );
+}
+
+export default App;