feat: add Matrix chat notification support (#211)

Implements native Matrix notification channel support, allowing users
to receive service alerts in any Matrix room via the Client-Server API.

Changes:
- server/service-operation/notification/matrix.go: new Matrix service
  implementing the NotificationService interface (PUT /_matrix/client/v3/...)
- server/service-operation/notification/types.go: add MatrixHomeserver,
  MatrixRoomID, MatrixAccessToken fields to AlertConfiguration
- server/service-operation/notification/manager.go: register MatrixService
- server/pb_migrations/1772200000_updated_alert_configurations_matrix.js:
  PocketBase migration adding matrix fields and notification_type value
- application: Matrix option in channel dialog with homeserver/room/token
  fields, tab filter, list display, type definitions and translations (en, km)
- application/public/upload/notification/matrix.png: Matrix channel icon

README.md

@@ -60,7 +60,7 @@ CheckCle is an Open Source solution for seamless, real-time monitoring of full-s
 - Infrastructure Server Monitoring, Supports Linux (🐧 Debian, Ubuntu, CentOS, Red Hat, etc.) and Windows (Beta). And Servers metrics like CPU, RAM, disk usage, and network activity) with an one-line installation angent script.
 - Schedule Maintenance & Incident Management
 - Operational Status / Public Status Pages
-- Notifications via email, Telegram, Discord, and Slack
+- Notifications via email, Telegram, Discord, Slack, Matrix, and more
 - Reports & Analytics
 - Settings Panel (User Management, Data Retention, Multi-language, Themes (Dark & Light Mode), Notification and channels and alert templates).