Fix Telegram dedup identity and legacy Markdown escaping

lib/alerts/telegram.mjs

@@ -744,7 +744,9 @@ Respond with ONLY valid JSON:
 
 function escapeMd(text) {
   if (!text) return '';
-  return text.replace(/([_*\[\]()~`>#+\-=|{}.!\\])/g, '\\$1');
+  // The bot sends alerts with legacy Markdown parse mode, not MarkdownV2.
+  // Escape only the characters that legacy Markdown actually treats as markup.
+  return text.replace(/([_*`\[])/g, '\\$1');
 }
 
 function parseJSON(text) {