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/server-threshold.ts

@@ -3,6 +3,7 @@ import { db } from "../../db";
 import { notifications } from "../../db/schema";
 import {
 	sendDiscordNotification,
+	sendMattermostNotification,
 	sendLarkNotification,
 	sendSlackNotification,
 	sendTelegramNotification,
@@ -35,6 +36,7 @@ export const sendServerThresholdNotifications = async (
 			discord: true,
 			telegram: true,
 			slack: true,
+			mattermost: true,
 			lark: true,
 		},
 	});
@@ -43,7 +45,7 @@ export const sendServerThresholdNotifications = async (
 	const typeColor = 0xff0000; // Rojo para indicar alerta
 
 	for (const notification of notificationList) {
-		const { discord, telegram, slack, lark } = notification;
+		const { discord, telegram, slack, mattermost, lark } = notification;
 
 		if (discord) {
 			const decorate = (decoration: string, text: string) =>
@@ -154,7 +156,15 @@ export const sendServerThresholdNotifications = async (
 			});
 		}
 
-		if (lark) {
+		if (mattermost) {
+			await sendMattermostNotification(mattermost, {
+				text: `**⚠️ Server ${payload.Type} Alert**\n\n**Server Name:** ${payload.ServerName}\n**Type:** ${payload.Type}\n**Current Value:** ${payload.Value.toFixed(2)}%\n**Threshold:** ${payload.Threshold.toFixed(2)}%\n**Message:** ${payload.Message}\n**Time:** ${date.toLocaleString()}`,
+				channel: mattermost.channel,
+				username: mattermost.username || "Dokploy",
+			});
+		}
+		
+				if (lark) {
 			await sendLarkNotification(lark, {
 				msg_type: "interactive",
 				card: {