[FEATURE]: Surface MCP tool progress in the TUI (revive #32480 with a dedicated progress event)

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Describe the enhancement you want to request

MCP servers commonly emit notifications/progress for long-running tools (30–180 s search over a large index, reindex, etc.). Since #32477 the client receives those notifications and resets the per-request timeout, but nothing is shown in the UI: the tool card keeps a bare spinner, so users can't tell "working" from "hung". Verified on 1.18.31 against a local streamable-http server — the server sees _meta.progressToken and its notifications are delivered, the TUI just ignores them.

What I'd like: render the running tool's progress in the TUI (e.g. In progress [N/M] · message on the tool card), using a dedicated event so it isn't confused with streamed partial tool output (session.next.tool.progress).

Prior art: #26328 (design + plan, closed by the stale bot) and #32480 (implementation, auto-closed during PR cleanup — the open question there was exactly the event name). Happy to rebase #32480 with a renamed event if a maintainer confirms the shape.

Start by reviewing the implementation history in #32480 and the notification handling described in #32477. Trace how MCP notifications reach the TUI and how the tool card handles streamed partial output. Done means the TUI displays MCP tool progress distinctly from partial tool output, with the event shape resolved.