Refactor app into components and add file upload progress

Components created:
- Header: App header with GitHub links
- ActionSelector: Step 1 - Choose create/join/scan
- MethodSelector: Step 2 - Choose connection method
- ConnectionForm: Step 3 - Enter connection details
- ChatView: Step 4 - Connected chat interface
- Message: Individual message display (text/file)
- QRScanner: QR code scanning component
- QRCodeDisplay: QR code display component
- FileUploadProgress: Progress bar for file uploads

Features:
- Clean component separation with props
- File upload progress bar with percentage
- Cancel upload functionality
- Disabled file button during upload
- Visual progress indicator with gradient
- All logic remains in App.jsx for state management

src/components/QRCodeDisplay.jsx

@@ -0,0 +1,13 @@
+function QRCodeDisplay({ qrCodeUrl, connectionId }) {
+  if (!qrCodeUrl) return null;
+
+  return (
+    <div className="qr-code-container">
+      <p className="qr-label">Scan to connect:</p>
+      <img src={qrCodeUrl} alt="Connection QR Code" className="qr-code" />
+      <p className="connection-id-display">{connectionId}</p>
+    </div>
+  );
+}
+
+export default QRCodeDisplay;