[Feat] show credit usage in chat responses and session popover

Is your feature request related to a problem? Please describe.
I can't see how many credits I've been using.

Describe the solution you'd like
I expect the credit usage to be shown similar to Copilot for VS Code:
https://code.visualstudio.com/docs/agents/guides/optimize-usage#_monitor-your-usage

In particular:

To view the cost for a single request, hover over the chat response to see the credit consumption for that turn.

and

The session info popover shows the total cost in credits and the cumulative context window token usage for the whole session

Describe alternatives you've considered
I have to run my prompt in VS Code if I want to see how many credits are being consumed by that prompt.

Additional context
Organizations on GitHub may configure a monthly credit limit. When that limit is reached then we start asking ourselves how we can watch how many credits each of us are consuming. Not being able to see the credit usage is problematic for developers using the Eclipse plugin.

Start by locating the Eclipse plugin's chat response rendering and session information popover, then trace how credit consumption and context-window usage are available to the UI. Done means a response hover shows per-turn credit usage and the session popover shows total credits and cumulative context tokens, with behavior comparable to the linked VS Code guidance.