feat: expose token used by AI agent

[aonnikov]

No description provided.

[ArtyomSavchenko]

@aonnikov Is this test failure related to the changes?

FAIL src/services/__tests__/llmService.test.ts
  ● DefaultLLMService › chat handles tool-call rounds and accumulates provider and tool usage

    expect(jest.fn()).toHaveBeenCalledWith(...expected)

    Expected: "Executing LLM tool", {"args": "{\"q\":\"x\"}", "round": 0, "tool": "lookup", "toolCallId": "call-1", "workspace": "00000000-0000-4000-8000-000000000001"}

    Number of calls: 0

      231 |       undefined
  ...7 lines omitted...
      at Object.<anonymous> (src/services/__tests__/llmService.test.ts:233:22)