Fixes#27210.
## Why
When the app server reports a visible `HookStarted` event for a
`PostToolUse` hook but the turn reaches `TurnCompleted` before a
matching hook completion event arrives, the TUI can leave the transient
`Running PostToolUse hook` row visible after the agent is done.
Interrupted and failed turn cleanup already drops transient live hook
rows; the normal completion path did not.
## What Changed
- Added `ChatWidget::clear_active_hook_cell()` for dropping transient
live hook status without writing it to history.
- Call that cleanup from normal task completion, while reusing it for
the existing start/finalize cleanup paths.
- Added `completed_turn_clears_visible_running_hook` snapshot coverage
for the reported `PostToolUse` case.
## Tests
- `just test -p codex-tui completed_turn_clears_visible_running_hook`
- `just test -p codex-tui` (fails on current `main` in unrelated
guardian tests:
`update_feature_flags_disabling_guardian_clears_review_policy_and_restores_default`
and
`update_feature_flags_disabling_guardian_clears_manual_review_policy_without_history`)
Mitsuhiro Kotake
44403dd3dd