Documents the Telegram webhook mode from #3880: - New 'Webhook Mode' section in telegram.md with polling vs webhook comparison, config table, Fly.io deployment example, troubleshooting - Add TELEGRAM_WEBHOOK_URL/PORT/SECRET to environment-variables.md - Add Telegram section to .env.example (existing + webhook vars) Co-authored-by: raulbcs <raulbcs@users.noreply.github.com>