chore(search): PR #219 회차 1 리뷰 반영 — 잔존 dead-cache 주석/help text 정리

리뷰어 지적 6건 + 전체-트리 grep 으로 추가 발견한 동일 부류 4건:
- search --trace help text(CLI main.rs + MCP search tool) "Bypasses cache"
  → "always a fresh retriever run" (없는 캐시 광고 제거)
- corpus_revision 의 실제 소비자는 incremental ingest 가 아니라 cursor
  pagination(stale_cursor) 임을 반영 — HANDOFF 노트 사실 정정 + ingest.rs
  bump 주석/warn 로그 + corpus_revision/search_lexical 테스트 주석 재서술
  (검증: cursor.rs + app.rs:327/333/498 가 유일 소비자, ingest 는 bump 만)
- bulk.rs "LRU cache amortize" → embedder cold-start 만 amortize
- app.rs lexical_index_version "search cache 무효화" 제거
- app-facade README 의 search cache bullet 을 "(제거됨 — 이력)" 표시

잔여 dead-cache 개념 참조 0건(active tree), clippy -D warnings 클린.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012Mc6W1fgsrbFKTsqA6P8La

docs/components/app-facade/README.md

@@ -177,6 +177,6 @@ flowchart LR
   - app skeleton + ingest wiring: [`tasks/p3/p3-5-app-wiring.md`](../../../tasks/p3/p3-5-app-wiring.md), [`tasks/p6/p6-4-image-ingest-wiring.md`](../../../tasks/p6/p6-4-image-ingest-wiring.md), [`tasks/p7/p7-3-pdf-ingest-wiring.md`](../../../tasks/p7/p7-3-pdf-ingest-wiring.md)
   - reset: [`tasks/p9/p9-fb-06-data-reset-command.md`](../../../tasks/p9/p9-fb-06-data-reset-command.md)
   - ingest progress / cancel: [`tasks/p9/p9-fb-03-tui-ingest-background.md`](../../../tasks/p9/p9-fb-03-tui-ingest-background.md), [`tasks/p9/p9-fb-04-ingest-cancellation.md`](../../../tasks/p9/p9-fb-04-ingest-cancellation.md)
-  - search cache: [`tasks/p9/p9-fb-19-search-cache.md`](../../../tasks/p9/p9-fb-19-search-cache.md)
+  - search cache (제거됨 — 이력): [`tasks/p9/p9-fb-19-search-cache.md`](../../../tasks/p9/p9-fb-19-search-cache.md)
   - chat session CLI: [`tasks/p9/p9-fb-18-cli-ask-session-repl.md`](../../../tasks/p9/p9-fb-18-cli-ask-session-repl.md)
 - HOTFIXES (P3-5/P4-3 `--config` 누락 + `*_with_config` 패턴, P7-3 storage UNIQUE bug, p9-fb-* 도그푸딩 후속): [`tasks/HOTFIXES.md`](../../../tasks/HOTFIXES.md)