ensure new users get a default collection on signup and any missing users get them too

app/models.py

@@ -506,10 +506,24 @@ class BookmarkCollections(Model):
 
     @classmethod
     def create_default(cls, user_id):
-        q = """INSERT INTO bookmark_collections (user_id, name, is_default, sort_order)
-        VALUES (?, "Bookmarks", 1, 0) RETURNING id
-        """
-        res = db.fetch_one(q, user_id)
+        return cls.create({
+            'user_id': user_id,
+            'name': 'Bookmarks',
+            'is_default': True,
+            'sort_order': 0,
+        })
+
+    @staticmethod
+    def get_users_without_default():
+        q = """
+            SELECT users.id FROM users
+            WHERE NOT EXISTS (
+                SELECT 1 FROM bookmark_collections bc
+                WHERE bc.user_id = users.id
+                AND bc.is_default = 1
+            )
+            """
+        return [row['id'] for row in db.query(q)]
 
     @classmethod
     def get_for_user(cls, user_id):