[Feature Request]: Show Background Agent Activity in the VS Code Chat

What feature would you like to see?

Currently, when the LLM launches one or more background agents to perform tasks, there is no visual indication in the chat that this work is in progress.

It would be helpful to display a status indicator in the chat that provides visibility into background agent activity, for example:

How many agents are currently running.
An indication that they are actively processing in the background.
A notification when an agent completes its work.
Optionally, a simple progress summary (e.g., "2 of 5 agents completed").

Providing this feedback would make the agent's behavior much more transparent, reduce the impression that the extension is idle during periods without visible output, and help users understand that work is actively being performed before the final response is generated.

This quality-of-life improvement would make the overall experience more predictable and increase user confidence in the background processes executed by the agent.

Additional information

No response

Start in the VS Code Chat entry point and trace where background agents are launched and where their completion events become available. Define the chat status states for running agents, completed agents, and overall progress, then verify that the indicator appears during background work and updates when agents finish.