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/index.css

@@ -514,6 +514,74 @@ input[type="text"]:disabled {
   transform: scale(1.05);
 }
 
+.file-upload-progress {
+  background: #f8f9fa;
+  border: 2px solid #667eea;
+  border-radius: 8px;
+  padding: 16px;
+  margin-bottom: 16px;
+}
+
+.file-upload-header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  margin-bottom: 12px;
+}
+
+.file-upload-name {
+  font-weight: 600;
+  color: #333;
+  font-size: 0.9rem;
+}
+
+.file-upload-cancel {
+  background: #dc3545;
+  color: white;
+  border: none;
+  width: 24px;
+  height: 24px;
+  border-radius: 50%;
+  font-size: 1.2rem;
+  line-height: 1;
+  cursor: pointer;
+  transition: all 0.2s;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 0;
+}
+
+.file-upload-cancel:hover {
+  background: #c82333;
+  transform: scale(1.1);
+}
+
+.progress-bar {
+  background: #e0e0e0;
+  border-radius: 8px;
+  height: 24px;
+  overflow: hidden;
+  position: relative;
+}
+
+.progress-bar-fill {
+  background: linear-gradient(90deg, #667eea 0%, #764ba2 100%);
+  height: 100%;
+  transition: width 0.3s ease;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  position: relative;
+}
+
+.progress-text {
+  color: white;
+  font-size: 0.75rem;
+  font-weight: 600;
+  text-shadow: 0 1px 2px rgba(0, 0, 0, 0.2);
+}
+
 .logs {
   margin-top: 24px;
   border-top: 2px solid #f0f0f0;