Refactor code structure for improved readability and maintainability

server/lib/schema.js

@@ -7,10 +7,16 @@ async function createUsersTable() {
             username VARCHAR(50) NOT NULL UNIQUE,
             name VARCHAR(120) NOT NULL,
             email VARCHAR(120) NOT NULL UNIQUE,
+            is_admin TINYINT(1) NOT NULL DEFAULT 0,
             password_hash VARCHAR(255) NOT NULL,
             created_at DATETIME DEFAULT CURRENT_TIMESTAMP
         ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
     `);
+
+    const [columns] = await db.query(`SHOW COLUMNS FROM users LIKE 'is_admin'`);
+    if (columns.length === 0) {
+        await db.query(`ALTER TABLE users ADD COLUMN is_admin TINYINT(1) NOT NULL DEFAULT 0 AFTER email`);
+    }
 }
 
 async function createLicensesTable() {