Replaced error_log calls with structured logging using the Logger class in DiscordChannel, SlackChannel, TelegramChannel, and WebhookChannel. Log success and error cases with relevant context for improved observability and debugging.
Introduces a new 'Webhook (Custom)' notification channel allowing users to send JSON payloads to any HTTP endpoint (e.g., n8n, Zapier, custom APIs). Updates the UI to support webhook configuration, adds backend validation, and implements the WebhookChannel for sending notifications. Documentation is updated with usage instructions and payload examples.
