Add password reset functionality and SMTP mailer class

- Implemented reset-password.php for users to reset their passwords securely.
- Added validation for reset tokens and password strength checks.
- Created mailer.php to handle sending emails via SMTP, including password reset and invitation emails.
- Integrated responsive HTML email templates for better user experience.

config/database.php

@@ -148,6 +148,7 @@ function ensure_tables_exist(PDO $pdo): void {
             "ALTER TABLE users ADD COLUMN avatar_url VARCHAR(255) NULL AFTER theme",
             "ALTER TABLE users ADD COLUMN backup_codes TEXT NULL AFTER two_factor_enabled",
             "ALTER TABLE board_card_schedules ADD UNIQUE KEY uk_sched_card (card_id)",
+            "CREATE TABLE IF NOT EXISTS `password_resets` (`id` INT AUTO_INCREMENT PRIMARY KEY, `email` VARCHAR(191) NOT NULL, `token` VARCHAR(64) NOT NULL UNIQUE, `expires_at` DATETIME NOT NULL, `used_at` DATETIME NULL, `created_at` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP, INDEX (`email`), INDEX (`token`)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci",
         ];
         foreach ($colUpgrades as $sql) {
             try {