feat: create admin user if not exsit

internal/db/sqlc/users.sql.go

@@ -90,6 +90,17 @@ func (q *Queries) GetUserByUsername(ctx context.Context, username string) (User,
 	return i, err
 }
 
+const countUsers = `-- name: CountUsers :one
+SELECT COUNT(*)::bigint AS count FROM users
+`
+
+func (q *Queries) CountUsers(ctx context.Context) (int64, error) {
+	row := q.db.QueryRow(ctx, countUsers)
+	var count int64
+	err := row.Scan(&count)
+	return count, err
+}
+
 const upsertUserByUsername = `-- name: UpsertUserByUsername :one
 INSERT INTO users (username, email, password_hash, role, display_name, avatar_url, is_active, data_root)
 VALUES (