fix(#1453): rewrite stale get-shit-done paths in Codex skill mirror on upgrade (#1491)

* fix(#1453): clean up stale get-shit-done paths in Codex skill mirror on upgrade

Extends planLegacyCleanup in gsd-core/bin/lib/legacy-cleanup.cjs to scan
skills/gsd-* subdirectories for .md files that still embed the pre-rename
get-shit-done/ path (e.g. ~/.agents/skills/gsd-docs-update/SKILL.md).
These stale copies are removed by cleanupLegacyGsdCc during the next
install/upgrade so Codex can no longer discover and select them.

Adds 5 regression tests to tests/issue-607-legacy-cleanup.test.cjs covering
the stale path detection, non-flagging of fresh skills and user-owned dirs,
and the end-to-end ~/.agents/skills scenario from the issue.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(#1453): add gsd-allow-legacy-name markers to intentional legacy name references

Comments and test descriptions in legacy-cleanup.cjs and its test file
legitimately cite the old 'get-shit-done' directory name to explain what
the cleanup logic removes. Add the lint-exemption marker to each line so
lint-legacy-dir-name passes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

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

.changeset/sturdy-wasps-sprint.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 1453
+---
+clean up stale get-shit-done paths in Codex and Kimi skill mirrors on upgrade (#1453)