* feat(tui): detach foreground tasks to background with Ctrl+B
- Add Ctrl+B shortcut to detach all foreground Bash/subagent tasks at once
- Show "Press Ctrl+B to run in background" hint in tool cards (Agent immediately, Bash after 10s) and in the agent group panel
- Mark detached foreground subagents as ◐ backgrounded instead of ✓ Completed
- Filter foreground tasks out of the /tasks panel (they appear after detach)
- Steer the model away from blocking on TaskOutput after a detach
* fix(tui): address Codex review on Ctrl+B detach
- Preserve `◐ backgrounded` for detached subagents inside AgentGroupComponent by reusing getDerivedSubagentPhase in getSubagentSnapshot
- Distinguish detached-from-foreground subagents from started-in-background ones so the latter still read as `done`
- Let Ctrl+B fall through to readline backward-char at the idle prompt instead of always consuming the key
* fix(tui): address follow-up Codex review on detach hints
- Auto-clear the "No foreground task running." hint via showDetachHint so it doesn't stick on the footer
- Don't clobber a newer transient hint (e.g. exit confirmation) when the detach hint timer fires
- Add FooterComponent.getTransientHint()
* fix(tui): address Codex review on backgrounded gating and /tasks counts
- Only mark foreground-running subagent cards as backgrounded (skip done/backgrounded cards so background resumes don't mutate older rows)
- Count /tasks header from the filtered (background-only) task set so foreground-only sessions don't read misleading counts
- Add terminating-state guard to skip ERR_STREAM_PREMATURE_CLOSE when a process is killed or times out
- Ensure timeout/kill reason is reported instead of the internal stream error
- Add changeset for agent-core and kimi-code
