feat: add mattermost notification provider

Add comprehensive Mattermost integration as a new notification provider:

## Backend Implementation:
- Add `mattermost` to notificationType enum and database schema
- Create mattermost table with webhookUrl, channel, username fields
- Implement CRUD operations: createMattermostNotification, updateMattermostNotification
- Add API routes: createMattermost, updateMattermost, testMattermostConnection
- Add sendMattermostNotification utility with proper payload formatting

## Frontend Implementation:
- Add MattermostIcon component with provided SVG logo
- Extend notification form with Mattermost schema validation
- Add webhook URL (required), channel and username (optional) form fields
- Integrate test connection functionality
- Add Mattermost to provider selection UI

## Notification Integration:
- Integrate across all notification types:
  - Build success/error notifications
  - Database backup notifications
  - Docker cleanup notifications
  - Dokploy restart notifications
  - Server threshold alerts
- Format messages using Markdown for Mattermost compatibility
- Handle optional channel (#prefix) and username override
- Graceful fallback for empty optional fields

## Features:
- Webhook-based messaging to Mattermost channels
- Optional channel targeting and custom username display
- Consistent formatting with other notification providers
- Full CRUD support with proper validation
- Test connection capability

Closes: Support for Mattermost team communication platform

# Conflicts:
#	apps/dokploy/components/dashboard/settings/notifications/handle-notifications.tsx
#	apps/dokploy/components/icons/notification-icons.tsx
#	apps/dokploy/server/api/routers/notification.ts
#	packages/server/src/db/schema/notification.ts
#	packages/server/src/services/notification.ts
#	packages/server/src/utils/notifications/build-error.ts
#	packages/server/src/utils/notifications/build-success.ts
#	packages/server/src/utils/notifications/database-backup.ts
#	packages/server/src/utils/notifications/docker-cleanup.ts
#	packages/server/src/utils/notifications/dokploy-restart.ts
#	packages/server/src/utils/notifications/server-threshold.ts
#	packages/server/src/utils/notifications/utils.ts

packages/server/src/utils/notifications/database-backup.ts

@@ -9,6 +9,7 @@ import {
 	sendEmailNotification,
 	sendLarkNotification,
 	sendGotifyNotification,
+	sendMattermostNotification,
 	sendNtfyNotification,
 	sendSlackNotification,
 	sendTelegramNotification,
@@ -45,13 +46,13 @@ export const sendDatabaseBackupNotifications = async ({
 			slack: true,
 			gotify: true,
 			ntfy: true,
+			mattermost: true,
 			lark: true,
 		},
 	});
 
 	for (const notification of notificationList) {
-		const { email, discord, telegram, slack, gotify, ntfy, lark } =
-			notification;
+		const { email, discord, telegram, slack, gotify, ntfy, mattermost, lark } = notification;
 
 		if (email) {
 			const template = await renderAsync(
@@ -356,5 +357,19 @@ export const sendDatabaseBackupNotifications = async ({
 				},
 			});
 		}
+		
+		if (mattermost) {
+			const statusEmoji = type === "success" ? "✅" : "❌";
+			const typeStatus = type === "success" ? "Successful" : "Failed";
+			const errorMsg = type === "error" && errorMessage
+				? `\n\n**Error:**\n\`\`\`\n${errorMessage}\n\`\`\``
+				: "";
+
+			await sendMattermostNotification(mattermost, {
+				text: `**${statusEmoji} Database Backup ${typeStatus}**\n\n**Project:** ${projectName}\n**Application:** ${applicationName}\n**Type:** ${databaseType}\n**Database Name:** ${databaseName}\n**Date:** ${format(date, "PP")}\n**Time:** ${format(date, "pp")}${errorMsg}`,
+				channel: mattermost.channel,
+				username: mattermost.username || "Dokploy",
+			});
+		}
 	}
 };