[feature] : preview for session message

[jensenojs]

Currently, when selecting a subagent for preview, only the session title and session ID are visible, but the specific conversation content cannot be seen.

In fact, this issue is not limited to selecting subagents.

If it is possible to provide some preview of message rendering within an acceptable time delay, it would be very helpful.

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now

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vibing ...

[jensenojs]

depend on #393 to simply

[jensenojs]

sth like

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