Implement scrolling through previous notes

lib/notes.dart

@@ -61,3 +61,42 @@ Future<Scratch?> getLatestScratch() async {
 Future<void> createScratch(String content) async {
   await DB.db.insert('scratches', {'content': content});
 }
+
+// Get the note immediately older than the given date
+Future<Note?> getPreviousNote(String currentDate) async {
+  final List<Map<String, dynamic>> notes = await DB.db.query(
+    'notes',
+    where: 'date < ?',
+    whereArgs: [currentDate],
+    orderBy: 'date DESC',
+    limit: 1,
+  );
+  if (notes.isNotEmpty) {
+    return Note(
+      date: notes.first['date'] as String,
+      content: notes.first['content'] as String,
+    );
+  }
+  return null;
+}
+
+// Get the note immediately newer than the given date
+Future<Note?> getNextNote(String currentDate) async {
+  final List<Map<String, dynamic>> notes = await DB.db.query(
+    'notes',
+    where: 'date > ?',
+    whereArgs: [currentDate],
+    orderBy: 'date ASC',
+    limit: 1,
+  );
+  if (notes.isNotEmpty) {
+    return Note(
+      date: notes.first['date'] as String,
+      content: notes.first['content'] as String,
+    );
+  }
+  // If there's no newer note, it means we might be at the latest
+  // but let's double-check by explicitly getting the latest again.
+  // This handles the case where the `currentDate` might not be the absolute latest.
+  return getLatestNote();
+}