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.

server/telegram.js

@@ -0,0 +1,49 @@
+/**
+ * Telegram Bot API — отправка уведомлений
+ */
+
+/**
+ * @param {string} token - Bot token from @BotFather
+ * @param {string|string[]} chatIds - Chat ID(s), comma-separated string or array
+ * @param {string} text - Message text
+ * @param {string|number} [messageThreadId] - ID топика в SuperGroup (для отправки в цепочку сообщений)
+ * @returns {Promise<void>}
+ */
+export async function sendTelegramMessage(token, chatIds, text, messageThreadId) {
+  if (!token?.trim() || !text?.trim()) return
+  const ids = Array.isArray(chatIds)
+    ? chatIds
+    : String(chatIds || '')
+        .split(',')
+        .map((id) => id.trim())
+        .filter(Boolean)
+  if (ids.length === 0) return
+
+  const threadId = messageThreadId != null && messageThreadId !== '' ? Number(messageThreadId) : null
+  const payload = {
+    text,
+    parse_mode: 'HTML',
+    disable_web_page_preview: true,
+  }
+  if (Number.isFinite(threadId)) payload.message_thread_id = threadId
+
+  const url = `https://api.telegram.org/bot${token.trim()}/sendMessage`
+  for (const chatId of ids) {
+    try {
+      const res = await fetch(url, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({
+          ...payload,
+          chat_id: chatId,
+        }),
+      })
+      const data = await res.json().catch(() => ({}))
+      if (!data.ok) {
+        console.warn(`Telegram sendMessage failed for chat ${chatId}:`, data.description || res.statusText)
+      }
+    } catch (err) {
+      console.warn(`Telegram sendMessage error for chat ${chatId}:`, err.message)
+    }
+  }
+}