Implement Telegram notification features for payment expiry and new tariffs

- Added functionality to send Telegram notifications for upcoming payment expirations and new tariffs.
- Enhanced `runScheduledSync` and `runScheduledSyncTariffs` to trigger notifications based on settings.
- Updated database schema to include Telegram settings and notification preferences.
- Introduced a test endpoint for verifying Telegram notification setup in the settings page.
- Improved user interface in the settings page to manage Telegram bot token and notification preferences.

src/lib/api.js

@@ -51,7 +51,14 @@ async function fetchApi(path, options = {}) {
     ...options,
   })
   if (!res.ok) {
-    const err = new Error(res.statusText || 'API error')
+    let message = res.statusText || 'API error'
+    try {
+      const data = await res.json()
+      if (data?.error) message = data.error
+    } catch {
+      /* ignore */
+    }
+    const err = new Error(message)
     err.status = res.status
     err.response = res
     throw err
@@ -156,3 +163,8 @@ export async function testApiConnection(apiBaseUrl, apiCredentials) {
 export async function fetchSyncStatus() {
   return fetchApi('/api/sync/status')
 }
+
+export async function sendTelegramTestNotification() {
+  const res = await fetchApi('/api/settings/telegram/test', { method: 'POST' })
+  return res
+}