Show the subagents in the clients

When a subagent starts a run, the terminal client and Telegram show
"[NAME] started". The terminal shows the whole report, which starts with
the name. Telegram shows only "[NAME] finished", "[NAME] stopped", or
"[NAME] failed", because the reply of the agent in the turn of the
report carries its content, and the phone then gets one message for each
result. Neither client shows the tool calls of a subagent.

The work event of a report gets the name of the subagent in its source
and the end of the run in a new status field, so that a client needs no
parse of the report text.

Issue: b1ac698