Add Pushover notification channel and improve status detection

Introduces Pushover as a new notification channel with priority-based alerts, device targeting, and custom sounds. Enhances domain status detection for .nl and .eu domains, ensuring accurate handling when expiration dates or explicit status flags are missing. Fixes PHP 8.x compatibility issues with null parameters in date functions and improves error handling and logging by replacing error_log() with a centralized Logger service. Updates documentation and migrations for version 1.1.1.

database/migrations/000_initial_schema_v1.1.0.sql

@@ -225,7 +225,7 @@ ON DUPLICATE KEY UPDATE color = VALUES(color), description = VALUES(description)
 CREATE TABLE IF NOT EXISTS notification_channels (
     id INT AUTO_INCREMENT PRIMARY KEY,
     notification_group_id INT NOT NULL,
-    channel_type ENUM('email', 'telegram', 'discord', 'slack', 'mattermost', 'webhook') NOT NULL,
+    channel_type ENUM('email', 'telegram', 'discord', 'slack', 'mattermost', 'webhook', 'pushover') NOT NULL,
     channel_config JSON NOT NULL,
     is_active BOOLEAN DEFAULT TRUE,
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
@@ -362,7 +362,7 @@ INSERT INTO settings (setting_key, setting_value, `type`, `description`) VALUES
 ('app_name', 'Domain Monitor', 'string', 'Application name'),
 ('app_url', 'http://localhost:8000', 'string', 'Application URL'),
 ('app_timezone', 'UTC', 'string', 'Application timezone'),
-('app_version', '1.1.0', 'string', 'Application version number'),
+('app_version', '1.1.1', 'string', 'Application version number'),
 
 -- Email settings
 ('mail_host', 'smtp.mailtrap.io', 'string', 'SMTP server host'),