fix(telegram): cron and heartbeat messages land in wrong chat instead of target topic (#19367)

Merged via /review-pr -> /prepare-pr -> /merge-pr.

Prepared head SHA: bf02bbf9cec2aacbc909905fad90450cc7d921ec
Co-authored-by: Lukavyi <1013690+Lukavyi@users.noreply.github.com>
Co-authored-by: obviyus <22031114+obviyus@users.noreply.github.com>
Reviewed-by: @obviyus

docs/gateway/heartbeat.md

@@ -176,7 +176,7 @@ Use `accountId` to target a specific account on multi-account channels like Tele
         heartbeat: {
           every: "1h",
           target: "telegram",
-          to: "12345678",
+          to: "12345678:topic:42", // optional: route to a specific topic/thread
           accountId: "ops-bot",
         },
       },
@@ -205,7 +205,7 @@ Use `accountId` to target a specific account on multi-account channels like Tele
   - `last` (default): deliver to the last used external channel.
   - explicit channel: `whatsapp` / `telegram` / `discord` / `googlechat` / `slack` / `msteams` / `signal` / `imessage`.
   - `none`: run the heartbeat but **do not deliver** externally.
-- `to`: optional recipient override (channel-specific id, e.g. E.164 for WhatsApp or a Telegram chat id).
+- `to`: optional recipient override (channel-specific id, e.g. E.164 for WhatsApp or a Telegram chat id). For Telegram topics/threads, use `<chatId>:topic:<messageThreadId>`.
 - `accountId`: optional account id for multi-account channels. When `target: "last"`, the account id applies to the resolved last channel if it supports accounts; otherwise it is ignored. If the account id does not match a configured account for the resolved channel, delivery is skipped.
 - `prompt`: overrides the default prompt body (not merged).
 - `ackMaxChars`: max chars allowed after `HEARTBEAT_OK` before delivery.