feat(#1754): CLI version-skew detection — warn when a global install shadows project-local GSD (#1755)

* feat(#1754): CLI version-skew detection — warn when a global install shadows project-local GSD

Addresses #1754 (approved-enhancement). Detects when the running gsd-tools.cjs
is outside the project root while a project-local install exists — the shadowing
scenario from #1748 where a stale global canary CLI (retired @gsd-build/sdk)
silently overrides project-local GSD.

Implementation (Node CLI entry-point, not shell snippet — avoids bloating 93
workflow files past their size caps):

- src/cli-skew-check.cts: pure function checkCliSkew({resolvedPath, projectRoot,
  projectLocalExists}) → string|null. Compares paths via path.relative; returns
  a warning when the resolved CLI is outside the project root AND a project-local
  install exists. Includes @gsd-build/sdk removal hint when the path matches.
  No I/O (pure), no gsd-sdk literal (avoids bug-2801 lint).
- gsd-core/bin/gsd-tools.cjs: wired at startup via the existing findProjectRoot
  resolver. Non-blocking (try/catch; advisory stderr warning, never gates).
- eslint.config.mjs: registers the new ADR-457 generated artifact in the ignores.
- tests: 6-case suite (skew/no-skew/legacy/normalization); all green.
- Golden fixtures regenerated (UPDATE_GOLDEN=1) for the new compiled artifact.
- docs/how-to/update-gsd.md: Diátaxis reference note for the skew warning.

Full suite: 3354 pass, 0 regressions (1 pre-existing local AGENTS.md failure).
lint:ci green.

Closes #1754

* chore(#1754): backfill changeset pr placeholder

* chore(#1754): regenerate INVENTORY-MANIFEST for the new cli-skew-check source module

---------

Co-authored-by: review-bot <review-bot@gsd>

docs/INVENTORY-MANIFEST.json

@@ -299,6 +299,7 @@
       "check-command-router.cjs",
       "cjs-command-router-adapter.cjs",
       "cli-exit.cjs",
+      "cli-skew-check.cjs",
       "clock.cjs",
       "clusters.cjs",
       "code-review-flags.cjs",