feat(notifications): add Telegram notification channel (#2753)

Add Telegram as a new notification type, allowing users to receive
monitor alerts via a Telegram bot.

Configuration requires:
- Bot token (obtained from @BotFather)
- Chat ID (user, group, or channel)

Changes:
- TelegramProvider: sends HTML-formatted messages via Telegram Bot API
- NotificationsService: route telegram type to TelegramProvider
- Notification model/types: add 'telegram' to NotificationChannel enum
- Server validation: telegram schema (accessToken + address/chat_id)
- Client Types/Validation: telegram schema with accessToken + address
- useNotificationForm: handle telegram defaults
- Notifications create page: render Telegram config UI
- en.json: add telegram i18n keys

server/src/validation/notificationValidation.ts

@@ -65,6 +65,13 @@ export const createNotificationBodyValidation = z.discriminatedUnion("type", [
 		type: z.literal("teams"),
 		address: z.url({ message: "Please enter a valid Webhook URL" }),
 	}),
+	// Telegram notification
+	z.object({
+		notificationName: z.string().min(1, "Notification name is required"),
+		type: z.literal("telegram"),
+		address: z.string().min(1, "Chat ID is required"),
+		accessToken: z.string().min(1, "Bot token is required"),
+	}),
 ]);
 
 export const testNotificationBodyValidation = createNotificationBodyValidation;