AX Agent footer 작업 바 chip 스타일 통일 및 후속 polish

- ChatWindow에 FooterChipBtn 스타일을 추가해 하단 작업 바 버튼 언어를 공통화
- 권한과 Git 브랜치 버튼이 같은 라운드/테두리/패딩 규칙을 사용하도록 정리
- README와 DEVELOPMENT 문서에 2026-04-06 11:34 (KST) 기준 footer polish 반영
- dotnet build 검증 경고 0, 오류 0 확인

docs/DEVELOPMENT.md

@@ -4939,3 +4939,5 @@ ow + toggle ?쒓컖 ?몄뼱濡??ㅼ떆 ?뺣젹?덈떎.
 - Document update: 2026-04-06 11:20 (KST) - This is the first visual-language polish pass after the large structure split. It reduces the feeling that preview and file browser are separate widgets and makes future popup/surface refinements reusable.
 - Document update: 2026-04-06 11:27 (KST) - Continued popup visual-language unification by switching `ChatWindow.PopupPresentation.cs` to the shared surface helpers and aligning selection/permission rows in `ChatWindow.SelectionPopupPresentation.cs` and `ChatWindow.PermissionPresentation.cs` with the same border, hover, and selected-state rules.
 - Document update: 2026-04-06 11:27 (KST) - At this point preview, file browser, worktree chooser, and permission-mode popup surfaces all share nearly the same visual language; remaining work is minor spacing/color polish rather than another behavior or structure change.
+- Document update: 2026-04-06 11:34 (KST) - Added `FooterChipBtn` to `ChatWindow.xaml` and aligned the footer work-bar buttons (`권한`, `Git 브랜치`) to the same rounded border, padding, and hover language instead of mixing outline and ghost button styles.
+- Document update: 2026-04-06 11:34 (KST) - This is a footer polish follow-up after the structure split, aimed at making the bottom work bar feel like one coherent tool row rather than a set of unrelated controls.