Add agent host user message telemetry (#316797)

* Add agent host user message telemetry

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Propagate agent host telemetry level

Use root config to propagate the client telemetry level into the Agent Host process and clamp Agent Host telemetry to the most restrictive level. Also forwards parent process telemetry disablement into spawned Agent Host processes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Extract agent host telemetry reporter

Move the agentHostUserMessageSent event payload, classification, and publicLog2 call out of AgentSideEffects into a focused helper class.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Add agent host user message telemetry metadata

Rename the user-message event to agentHost.userMessageSent and include safe session and active-client metadata that is available at send time.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Trim agent host user message telemetry fields

Remove boolean fields that can be derived from turnCount, activeClientId, and attachmentCount.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix agent host telemetry ID classifications

Classify Agent Host protocol IDs as system metadata instead of end-user pseudonymized information.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>