sample json fix

lib/screens/deck_import_screen.dart

@@ -348,6 +348,7 @@ class _DeckImportScreenState extends State<DeckImportScreen> {
           'prompt': 'Sample Question $i?',
           'answers': ['Answer A', 'Answer B', 'Answer C', 'Answer D'],
           'correctAnswerIndices': [i % 4],
+          if (i == 0) 'explanation': 'Optional explanation shown when viewing question details after an attempt.',
           'isKnown': i < 5,
         };
       }),
@@ -502,24 +503,18 @@ class _DeckImportScreenState extends State<DeckImportScreen> {
                 child: Column(
                   crossAxisAlignment: CrossAxisAlignment.stretch,
                   children: [
-                    Row(
-                      mainAxisAlignment: MainAxisAlignment.spaceBetween,
-                      children: [
-                        Text(
-                          'Deck JSON',
-                          style: Theme.of(context).textTheme.titleMedium,
-                        ),
-                        Row(
-                          mainAxisSize: MainAxisSize.min,
+                    Wrap(
+                      spacing: 8,
+                      runSpacing: 4,
                       children: [
                         TextButton.icon(
                           onPressed: _pickJsonFile,
-                              icon: const Icon(Icons.folder_open),
+                          icon: const Icon(Icons.folder_open, size: 20),
                           label: const Text('Select file'),
                         ),
                         TextButton.icon(
                           onPressed: _loadSampleDeck,
-                              icon: const Icon(Icons.description),
+                          icon: const Icon(Icons.description, size: 20),
                           label: const Text('Load Sample'),
                         ),
                         IconButton(
@@ -529,8 +524,6 @@ class _DeckImportScreenState extends State<DeckImportScreen> {
                         ),
                       ],
                     ),
-                      ],
-                    ),
                     const SizedBox(height: 8),
                     TextField(
                       controller: _jsonController,