feat: add Telegram notification provider support

- Updated API to support Telegram as a notification provider type.
- Enhanced tests to cover Telegram provider creation, updates, and token handling.
- Modified frontend forms to include Telegram-specific fields and validation.
- Added localization strings for Telegram provider.
- Implemented security measures to ensure bot tokens are not exposed in API responses.

frontend/src/api/__tests__/notifications.test.ts

@@ -54,7 +54,8 @@ describe('notifications api', () => {
 
     await expect(createProvider({ name: 'x', type: 'slack' })).rejects.toThrow('Unsupported notification provider type: slack')
     await expect(updateProvider('2', { name: 'updated', type: 'generic' })).rejects.toThrow('Unsupported notification provider type: generic')
-    await expect(testProvider({ id: '2', name: 'test', type: 'telegram' })).rejects.toThrow('Unsupported notification provider type: telegram')
+    await testProvider({ id: '2', name: 'test', type: 'telegram' })
+    expect(client.post).toHaveBeenCalledWith('/notifications/providers/test', { id: '2', name: 'test', type: 'telegram' })
   })
 
   it('templates and previews use merged payloads', async () => {

frontend/src/api/notifications.test.ts

@@ -119,7 +119,52 @@ describe('notifications api', () => {
 
     await expect(createProvider({ name: 'Bad', type: 'slack' })).rejects.toThrow('Unsupported notification provider type: slack')
     await expect(updateProvider('bad', { type: 'generic' })).rejects.toThrow('Unsupported notification provider type: generic')
-    await expect(testProvider({ id: 'bad', type: 'telegram' })).rejects.toThrow('Unsupported notification provider type: telegram')
+  })
+
+  it('supports telegram provider with token payload contract', async () => {
+    mockedClient.post.mockResolvedValue({ data: { id: 'tg1' } })
+    mockedClient.put.mockResolvedValue({ data: { id: 'tg1' } })
+
+    await createProvider({ name: 'Telegram', type: 'telegram', gotify_token: 'bot123:ABC' })
+    expect(mockedClient.post).toHaveBeenCalledWith('/notifications/providers', {
+      name: 'Telegram',
+      type: 'telegram',
+      token: 'bot123:ABC',
+    })
+
+    await updateProvider('tg1', { type: 'telegram', url: '987654321', gotify_token: 'newtoken' })
+    expect(mockedClient.put).toHaveBeenCalledWith('/notifications/providers/tg1', {
+      type: 'telegram',
+      url: '987654321',
+      token: 'newtoken',
+    })
+
+    await updateProvider('tg1', { type: 'telegram', url: '987654321' })
+    expect(mockedClient.put).toHaveBeenCalledWith('/notifications/providers/tg1', {
+      type: 'telegram',
+      url: '987654321',
+    })
+  })
+
+  it('telegram preserves token in sanitization and strips gotify_token key', async () => {
+    mockedClient.post.mockResolvedValue({ data: { id: 'tg2' } })
+
+    await createProvider({ name: 'TG', type: 'telegram', token: 'direct-token', gotify_token: '' })
+    expect(mockedClient.post).toHaveBeenCalledWith('/notifications/providers', {
+      name: 'TG',
+      type: 'telegram',
+      token: 'direct-token',
+    })
+  })
+
+  it('telegram test/preview strips token from read-like actions', async () => {
+    mockedClient.post.mockResolvedValue({ data: { id: 'tg3' } })
+
+    await testProvider({ id: 'tg3', type: 'telegram', gotify_token: 'should-not-send' })
+    expect(mockedClient.post).toHaveBeenCalledWith('/notifications/providers/test', {
+      id: 'tg3',
+      type: 'telegram',
+    })
   })
 
   it('fetches templates and previews provider payloads with data', async () => {

frontend/src/api/notifications.ts

@@ -1,6 +1,6 @@
 import client from './client';
 
-export const SUPPORTED_NOTIFICATION_PROVIDER_TYPES = ['discord', 'gotify', 'webhook', 'email'] as const;
+export const SUPPORTED_NOTIFICATION_PROVIDER_TYPES = ['discord', 'gotify', 'webhook', 'email', 'telegram'] as const;
 export type SupportedNotificationProviderType = (typeof SUPPORTED_NOTIFICATION_PROVIDER_TYPES)[number];
 const DEFAULT_PROVIDER_TYPE: SupportedNotificationProviderType = 'discord';
 
@@ -59,7 +59,7 @@ const sanitizeProviderForWriteAction = (data: Partial<NotificationProvider>): Pa
 
   delete payload.gotify_token;
 
-  if (type !== 'gotify') {
+  if (type !== 'gotify' && type !== 'telegram') {
     delete payload.token;
     return payload;
   }