Generate automatic and manual conversation recaps (#40705)

## Why

Users returning to a conversation need a short summary of its recent progress and next steps.

## What changed

- Generate a recap for eligible idle, unfocused conversations and add it to the transcript.
- Add `/recap` to request the same summary on demand, with visible progress and actionable errors.
- Keep recap requests bounded and isolated, reject stale results, and retry only automatic failures.

## Testing

- Cover automatic and manual generation, request eligibility, failure handling, loading-state cleanup, and temporary-thread configuration.

GitOrigin-RevId: 926a88d6996d67a42809ce2c4091b13fca882b52

codex-rs/tui/src/bottom_pane/snapshots/codex_tui__bottom_pane__command_popup__tests__command_popup_default_items.snap

@@ -23,6 +23,7 @@ expression: commands
 /app - continue this session in the Desktop app
 /init - create an AGENTS.md file with instructions for Codex
 /compact - summarize conversation to prevent hitting the context limit
+/recap - summarize the current conversation now
 /agents - view and switch between all active agent sessions
 /side - start a side conversation in an ephemeral fork
 /copy - copy the last response, code block, or quote