* fix(artifacts): register RETROSPECTIVE.md as canonical planning artifact Adds RETROSPECTIVE.md to CANONICAL_EXACT in artifacts.cjs so gsd-health no longer raises W019 after any /gsd-complete-milestone run. The file was established as a living artifact in PR #644 but omitted from the W019 registry created in PR #2488. Closes #3198 * chore(changeset): point pr metadata to #3200