Implement CreateNote

internal/repository/notes.go

@@ -15,5 +15,11 @@ func NewNoteRepository(store NoteStore) *NoteRepository {
 }
 
 func (r *NoteRepository) CreateNote(content string) (models.Note, error) {
-	return models.Note{}, fmt.Errorf("not implemented")
+	if content == "" {
+		return models.Note{}, fmt.Errorf("content cannot be empty")
+	}
+	note := models.Note{
+		Content: content,
+	}
+	return r.store.SaveNote(note)
 }