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.

internal/preset/preset.go

@@ -352,7 +352,10 @@ func defaultAgentPresets() []*Preset {
   "ready_signal": { "idle_ms": 1000 },
   "idle_detection": {
     "strategy": "osc_title_stability",
-    "idle_threshold_ms": 2000
+    "idle_threshold_ms": 2000,
+    "thinking_patterns": [
+      "(?i)esc to interrupt"
+    ]
   },
   "chrome_trim_hints": [
     "^OpenAI Codex",