recorder: focus poller PoC for Gap I-1 (deferred, #14)

Adds a background focus poller that periodically calls
Automation.FocusedElement() and stamps the path onto key_down RawEvents,
so DragCollapser can fill type-step targets without relying on the stale
post-hoc Resolve() pass. Plumbing:

  Program.cs   — focus poller Task + diagnostic counters
  LowLevelHook — volatile CurrentFocusedPath, stamped on key_down
  RawEvent     — FocusedElementPath already existed (focus_change)
  DragCollapser— typeFocusPath captured at first printable key_down,
                 takes precedence over lastFocusPath/lastMousePath

Result on box-v7.yaml live recording: null_target_steps unchanged (13).
Root cause: EG-BIM Modeler's CommandBox and similar input controls lack
AutomationPeer, so UIA-based focus tracking — from any external process —
cannot see them. The WPF-internal Keyboard.FocusedElement is in-process
only and unreachable from the recorder.

Deferred. The plumbing stays in place because the same stamping path can
be reused by a future generic WPF DLL-injection probe. Player's existing
null-target fallback (Type→OS focus, Click→raw_coord) remains the official
strategy and successfully replays box-v7 end-to-end.

See docs/history/2026-04-08_gap-i1-deferred.md for analysis and future
options (generic WPF injection / AutomationPeer AI attachment).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

PLAN.md

@@ -10,8 +10,8 @@
 
 ## P1 — 라이브 검증 (사용자 환경 필요)
 
-4. **recorder Gap I-1** — type 스텝 target을 `Automation.FocusedElement`로 직접 채워 null_target_steps=0 달성. Player fallback 의존도 줄이기.
-5. **engine-bridge v3** — ReflectionEngineStateProvider 실매핑 (smoke test 이후)
+4. **engine-bridge v3** — `ReflectionEngineStateProvider` 실매핑. v2의 plugin masquerade + HttpListener 위에 카메라/선택/씬그래프 상태를 reflection으로 노출. 골든파일 sidecar JSON. `/contract engine-bridge-v3`.
+5. ~~recorder Gap I-1~~ — **deferred**. UIA poller PoC 결과 본질적 한계 확인 (AutomationPeer 부재 컨트롤은 못 봄). generic WPF DLL injection 또는 AutomationPeer AI 부착 PoC가 선결.
 
 ## Follow-ups (non-blocking)