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/db/schema/notification.ts

@@ -12,6 +12,7 @@ export const notificationType = pgEnum("notificationType", [
 	"email",
 	"gotify",
 	"ntfy",
+	"mattermost",
 	"lark",
 ]);
 
@@ -49,6 +50,9 @@ export const notifications = pgTable("notification", {
 	ntfyId: text("ntfyId").references(() => ntfy.ntfyId, {
 		onDelete: "cascade",
 	}),
+	mattermostId: text("mattermostId").references(() => mattermost.mattermostId, {
+		onDelete: "cascade",
+	}),
 	larkId: text("larkId").references(() => lark.larkId, {
 		onDelete: "cascade",
 	}),
@@ -120,6 +124,16 @@ export const ntfy = pgTable("ntfy", {
 	priority: integer("priority").notNull().default(3),
 });
 
+export const mattermost = pgTable("mattermost", {
+	mattermostId: text("mattermostId")
+		.notNull()
+		.primaryKey()
+		.$defaultFn(() => nanoid()),
+	webhookUrl: text("webhookUrl").notNull(),
+	channel: text("channel"),
+	username: text("username"),
+});
+
 export const lark = pgTable("lark", {
 	larkId: text("larkId")
 		.notNull()
@@ -153,6 +167,10 @@ export const notificationsRelations = relations(notifications, ({ one }) => ({
 		fields: [notifications.ntfyId],
 		references: [ntfy.ntfyId],
 	}),
+	mattermost: one(mattermost, {
+		fields: [notifications.mattermostId],
+		references: [mattermost.mattermostId],
+	}),
 	lark: one(lark, {
 		fields: [notifications.larkId],
 		references: [lark.larkId],
@@ -349,6 +367,49 @@ export const apiTestNtfyConnection = apiCreateNtfy.pick({
 	priority: true,
 });
 
+export const apiCreateMattermost = notificationsSchema
+	.pick({
+		appBuildError: true,
+		databaseBackup: true,
+		dokployRestart: true,
+		name: true,
+		appDeploy: true,
+		dockerCleanup: true,
+		serverThreshold: true,
+	})
+	.extend({
+		webhookUrl: z.string().min(1),
+		channel: z.string().optional(),
+		username: z.string().optional(),
+	})
+	.required({
+		name: true,
+		webhookUrl: true,
+		appBuildError: true,
+		databaseBackup: true,
+		dokployRestart: true,
+		appDeploy: true,
+		dockerCleanup: true,
+		serverThreshold: true,
+	});
+
+export const apiUpdateMattermost = apiCreateMattermost.partial().extend({
+	notificationId: z.string().min(1),
+	mattermostId: z.string().min(1),
+	organizationId: z.string().optional(),
+});
+
+export const apiTestMattermostConnection = apiCreateMattermost
+	.pick({
+		webhookUrl: true,
+		channel: true,
+		username: true,
+	})
+	.extend({
+		channel: z.string().optional(),
+		username: z.string().optional(),
+	});
+
 export const apiFindOneNotification = notificationsSchema
 	.pick({
 		notificationId: true,