런처 색인 영속 캐시와 증분 갱신 구조 적용

런처 색인 구조를 전체 재색인 중심에서 영속 캐시와 watcher 증분 반영 방식으로 재구성했다.

IndexService에 launcher-index.json 기반 캐시 로드/저장, 파일 생성·삭제·이름변경 증분 갱신, 디렉터리 고위험 변경 시 전체 재색인 폴백을 추가했다.

App 시작 시 캐시 로드와 파일 감시를 바로 시작하고, 무거운 전체 스캔은 실제 검색 시 한 번만 보강 실행하도록 정리했다.

README와 DEVELOPMENT 문서를 2026-04-06 18:24 (KST) 기준으로 갱신했고, Release 빌드 검증에서 경고 0 / 오류 0을 확인했다.

docs/DEVELOPMENT.md

@@ -4999,3 +4999,6 @@ ow + toggle ?쒓컖 ?몄뼱濡??ㅼ떆 ?뺣젹?덈떎.
 - Document update: 2026-04-06 18:02 (KST) - Hardened vLLM response handling for IBM deployment endpoints by accepting `results[].generated_text`, `output_text`, and `choices[].message.content`, and by short-circuiting tool-use requests in `LlmService.ToolUse.cs` with a `ToolCallNotSupportedException` so IBM deployment chat connections do not receive an incompatible OpenAI function-calling payload.
 - Document update: 2026-04-06 18:09 (KST) - Reworked message feedback toggles in `ChatWindow.MessageInteractions.cs`. `좋아요/싫어요` no longer keep separate local state with sibling reset callbacks; both buttons now derive from one shared `like/dislike/null` state and persist that single value back to the conversation/session.
 - Document update: 2026-04-06 18:09 (KST) - The feedback buttons now use the same glyph in both idle/active states and express activation through color plus rounded chip background/border, which avoids cases where the like filled-glyph was visually missing and ensures pressing `싫어요` again properly returns the message to an unselected state.
+- Document update: 2026-04-06 18:24 (KST) - Reworked launcher indexing in `IndexService.cs` from a “full rebuild on every change” structure to a persisted cache plus incremental watcher model. Launcher file-system entries are now saved to `%APPDATA%\AxCopilot\index\launcher-index.json`, loaded immediately at startup, and merged with aliases/built-in app entries before the first search.
+- Document update: 2026-04-06 18:24 (KST) - `FileSystemWatcher` changes are now handled incrementally where possible. File create/delete/rename events update only the affected launcher index entries and debounce cache persistence, while high-impact directory rename/delete cases still fall back to a full rebuild for correctness.
+- Document update: 2026-04-06 18:24 (KST) - `App.xaml.cs` now restores eager cache availability by calling `LoadCachedIndex()` and `StartWatchers()` at startup, while keeping the heavier full scan on the existing `EnsureIndexWarmupStarted()` path. This keeps the launcher responsive from the first open without reintroducing continuous full rescans as idle background work.