AX Agent footer와 Git 브랜치 프레젠테이션 구조를 분리하고 회귀 점검 루틴을 고정한다

- ChatWindow.FooterPresentation에서 Git 브랜치 팝업 렌더와 요약 helper를 분리해 폴더 바 상태/프리셋 안내 동기화 책임만 남긴다

- ChatWindow.GitBranchPresentation을 추가해 브랜치 팝업 조립, 요약 pill, 최근 브랜치/전환 액션 렌더를 별도 프레젠테이션 계층으로 옮긴다

- AX_AGENT_REGRESSION_PROMPTS 문서를 재작성해 실패 분류와 Chat/Cowork/Code별 필수 회귀 묶음을 개발 루틴으로 고정한다

- 검증: dotnet build src/AxCopilot/AxCopilot.csproj -c Release -v minimal -p:OutputPath=bin\\verify\\ -p:IntermediateOutputPath=obj\\verify\\ (경고 0 / 오류 0)

docs/DEVELOPMENT.md

@@ -4917,3 +4917,5 @@ ow + toggle ?쒓컖 ?몄뼱濡??ㅼ떆 ?뺣젹?덈떎.
 - Document update: 2026-04-06 09:36 (KST) - Removed the stale `Plan` option from `PermissionModePresentationCatalog.cs` and simplified `ChatWindow.PermissionPresentation.cs` so the permission popup and top-banner presentation only expose the live modes (`권한 요청`, `편집 자동 승인`, `권한 건너뛰기`, `읽기 전용`).
 - Document update: 2026-04-06 09:44 (KST) - Split inline interaction rendering further by replacing `ChatWindow.InlineInteractions.cs` with `ChatWindow.UserAskPresentation.cs` and `ChatWindow.PlanApprovalPresentation.cs`. User-question cards and plan approval/detail flows now live in dedicated partials instead of sharing one mixed interaction file.
 - Document update: 2026-04-06 09:44 (KST) - At this point the completed structure-improvement items are: status presentation cataloging, permission/tool-result catalog enrichment, permission UI cleanup, and ask/plan renderer separation. The remaining larger tracks are footer/composer work-bar refinement and enforcing the regression prompt ritual in day-to-day development.
+- Document update: 2026-04-06 09:58 (KST) - Split Git branch popup assembly and footer-adjacent summary helpers out of `ChatWindow.FooterPresentation.cs` into `ChatWindow.GitBranchPresentation.cs`. The footer presentation partial now focuses on folder-bar state and selected-preset guide synchronization instead of mixed popup rendering.
+- Document update: 2026-04-06 09:58 (KST) - Rewrote `docs/AX_AGENT_REGRESSION_PROMPTS.md` into a repeatable regression ritual with explicit failure classes (`blank-reply`, `duplicate-banner`, `bad-approval-flow`, `queue-drift`, `restore-drift`, `status-noise`) and required prompt bundles per change area so runtime/transcript work can be validated consistently.