fix: add missing email column to users table

init.sql

@@ -43,6 +43,7 @@ CREATE TABLE IF NOT EXISTS users (
     id INT AUTO_INCREMENT PRIMARY KEY,
     username VARCHAR(100) UNIQUE NOT NULL,
     password_hash VARCHAR(255) NOT NULL,
+    email VARCHAR(255),
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
 ) ENGINE=InnoDB;