fix(quick): port history-based resurrection guard from execute-phase.md (#3195) (#3201)

Replace the inverted PRE_MERGE_FILES grep in the worktree-merge cleanup
block with the git-log --diff-filter=D history check introduced for
execute-phase.md by PR #2510. The old form deleted any .planning/ file
absent from the pre-merge snapshot — including brand-new files such as
SUMMARY.md — rather than only files with a confirmed deletion event on
main. Remove the now-unused PRE_MERGE_FILES snapshot line. Adds a
drift-guard test (node:test) asserting both workflows use WAS_DELETED and
neither uses the bare PRE_MERGE_FILES grep form.

Closes #3195

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -8,6 +8,7 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Fixed
 
+- **`/gsd-quick` worktree-merge resurrection guard no longer deletes brand-new `.planning/` files** — the inverted `PRE_MERGE_FILES` grep that caused any file absent from the pre-merge snapshot (including freshly created `SUMMARY.md`) to be deleted has been replaced with the git-history check already used by `execute-phase.md` since PR #2510; only files with a confirmed deletion event in main's ancestry are now removed. (#3195)
 - **Milestone-archive layout support** — `validate consistency`, `validate health`, and `find-phase` now scan `.planning/milestones/v*-phases/` directories in addition to the flat `.planning/phases/` layout. Projects that have graduated to milestone-archive layout no longer receive spurious W006 "Phase N in ROADMAP.md but no directory on disk" warnings for every active phase. (#3164)
 
 ### Feature