Enable log rotation on Agent Sessions output channel

The Agent Sessions output channel was registered with \log: false\, which
uses FileOutputChannelModel backed by a logger with \donotRotate: true\.
Under \--log trace\, \logAllStatsIfTrace()\ dumps all sessions on every
resolution cycle (throttled to 500ms), causing unbounded file growth.

In three observed incidents, this contributed to 30+ MB log files and
renderer memory reaching the 15.7 GB V8 heap limit. The output channel
contents are loaded into a text model when visible, amplifying the
memory impact.

Switch to \log: true\ so the channel uses the standard logging
infrastructure with file rotation, preventing unbounded growth.

Co-authored-by: Copilot <[email protected]>