feat: notify admin via Telegram on webhook errors

Send error details to ADMIN_CHAT_ID (optional secret) whenever the
statuspage webhook handler hits an error path. Uses waitUntil() so
the notification never blocks the 200 response.

wrangler.jsonc

@@ -41,4 +41,5 @@
 	// Secrets (set via `wrangler secret put`):
 	// BOT_TOKEN - Telegram bot token
 	// WEBHOOK_SECRET - Statuspage webhook URL secret
+	// ADMIN_CHAT_ID - Telegram chat ID to receive error notifications
 }