Hold codex in thinking while a turn is running

Codex uses the osc_title_stability idle strategy, but it draws its
progress in the pane body ('Working … esc to interrupt'), not the OSC
title. The title goes stable mid-turn, so ~2s later the classifier
declared codex idle while it was still working. Add a thinking-promoter
pattern ((?i)esc to interrupt) to the codex built-in preset; classify()
checks promoter regexes against the rendered screen before the
title-stability verdict, so codex stays in thinking until the turn's
in-progress footer actually disappears.

Resolves the [CODEX IDLE] TODO item.

CHANGELOG.md

@@ -16,6 +16,8 @@ loosely follows [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   over MCP.
 
 ### Fixed
+- Codex agents are no longer reported idle while a turn is still
+  running.
 - Slow MCP tool calls such as `wait_for_pattern` no longer block later
   tool calls on the same MCP connection.
 - Closing an agent now escalates from SIGTERM to SIGKILL when needed,