Add master-detail layout for Notes and Chat on wide screens

On screens ≥600dp, Notes and Chat show a two-pane layout:
- Left pane (300dp): scrollable list with selection highlight
- Right pane: inline detail (NoteDetailScreen / ChatScreen)

Tapping a list item selects it in wide mode instead of pushing a route.
Creating a new conversation on wide screen auto-selects it in the pane.
Deleting a selected note/conversation clears the right pane.
NoteDetailScreen gains an optional onDeleted callback used by the
embedded pane to clear selection rather than call context.pop().
Tasks keep push-based navigation (edit form has save/pop semantics
that require a full-screen context).

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

lib/screens/notes/note_detail_screen.dart

@@ -8,7 +8,9 @@ import '../../providers/notes_provider.dart';
 
 class NoteDetailScreen extends ConsumerWidget {
   final int noteId;
-  const NoteDetailScreen({super.key, required this.noteId});
+  // Provided when embedded in master-detail: called instead of context.pop().
+  final VoidCallback? onDeleted;
+  const NoteDetailScreen({super.key, required this.noteId, this.onDeleted});
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
@@ -51,7 +53,9 @@ class NoteDetailScreen extends ConsumerWidget {
                     );
                     if (confirm == true) {
                       await ref.read(notesProvider.notifier).delete(noteId);
-                      if (context.mounted) context.pop();
+                      if (context.mounted) {
+                        onDeleted != null ? onDeleted!() : context.pop();
+                      }
                     }
                   },
                 ),