fix(tui): refresh working status when tools finish

[MelodyVAR]

When a tool finishes before the next assistant output, the Step working indicator keeps showing Running..., Reading..., or Editing.... The tool result and spinner are already complete, but the tool-verb hold remains set, so a slow next response looks like a tool that is still running.

Release that hold and clear the previous reasoning phase on tool_execution_end, then refresh the indicator after stopping the completed tool's spinner. Any remaining parallel tool keeps its own active verb; otherwise the indicator returns to Working... while preserving elapsed time and token counts.

This fixes the reproducible status display issue. The separately reported 30–60 second execution delay was not reproduced and is not claimed fixed by this PR.

Validation:

• Seven new event-to-render regression cases cover successful and failed run/read/edit completion, a simulated minute without further model output, and switching to a remaining parallel tool.
• All 41 tests in the seven related UI test files pass.
• npm run check passes.
• ./test.sh passes on Node 22.19.0, including the offline build and all workspace test suites (credential-dependent tests are skipped by the isolated runner).