Fix spinner/Esc interrupt when MCP startup completes mid-turn

[2mawi2]

Fixes #7017

What

• Prevent MCP startup completion from clearing the "task running" UI state during an active agent turn (spinner/status indicator stays visible; Esc interrupt keeps working).

Why

• McpStartupComplete could call bottom_pane.set_task_running(false) while an agent turn was still running, hiding the status indicator and disabling Esc interrupt.

How

• Track agent_turn_running separately and set effective running state as agent_turn_running || mcp_startup_status.is_some() (applied to both codex-rs/tui and codex-rs/tui2).
• Add regression tests ensuring McpStartupComplete does not clear task_running/status indicator after TaskStarted.

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[2mawi2]

I have read the CLA Document and I hereby sign the CLA

[etraut-openai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Nice work!

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[etraut-openai]

@2mawi2, thanks for the contribution. Sorry for the slow reply — we got behind over the holidays, but we're now back and going through the queue.

Could you please fix the merge conflicts?

[2mawi2]

@etraut-openai done and tested one more time!