[Bug][Telegram] Investigate api.telegram.org UnknownHostException

[NGirchev]

Imported from TODO.md:189-191.

Observed log:
2026-04-11 10:56:21.190 [opendaimon_bot Telegram Connection] ERROR o.t.t.u.DefaultBotSession - api.telegram.org
java.net.UnknownHostException: api.telegram.org

Acceptance criteria:

• Determine whether this is infrastructure/DNS-only or needs application-level retry/visibility.
• Add logging/retry behavior if the app can handle it better.
• Document operational remediation if it is purely environment-level.