Fix black screen and failed delete when confirming note deletion

The dialog builder was discarding its own context (_) and calling
Navigator.pop(context, ...) with the outer screen context instead.
This popped NoteDetailScreen off the navigator instead of closing the
dialog, causing a black screen and returning null to showDialog so the
delete operation never ran.

Fix: use dialogContext in the builder and pop that instead.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/screens/notes/note_detail_screen.dart

@@ -54,15 +54,17 @@ class NoteDetailScreen extends ConsumerWidget {
                   onPressed: () async {
                     final confirm = await showDialog<bool>(
                       context: context,
-                      builder: (_) => AlertDialog(
+                      builder: (dialogContext) => AlertDialog(
                         title: const Text('Delete note?'),
                         actions: [
                           TextButton(
-                            onPressed: () => Navigator.pop(context, false),
+                            onPressed: () =>
+                                Navigator.pop(dialogContext, false),
                             child: const Text('Cancel'),
                           ),
                           TextButton(
-                            onPressed: () => Navigator.pop(context, true),
+                            onPressed: () =>
+                                Navigator.pop(dialogContext, true),
                             child: const Text('Delete'),
                           ),
                         ],