chore: drop upstream gsd issue and pr governance

MSD does not use an issue tracker, and the inherited GSD community gates
auto-closed PR #1 for lacking an issue-numbered title. Remove them:

- workflows: require-issue-link, pr-title-validator,
  auto-close-unsolicited-prs, pr-template-format, close-draft-prs(-sweep),
  auto-label-issues, auto-branch, duplicate-check, duplicate-sweep,
  remove-duplicate-label
- GSD PR and issue templates, plus the scripts only they used
  (require-issue-link-policy, pr-template-policy, pr-changed-files) and
  their tests
- workflow lists in ci-test-scope, ci-pr-mergeability,
  workflow-maintainer-skip, lint-pr-check-project-dir, the docs-guard
  baseline and the conformance tiers
- CONTRIBUTING: PR-against-next flow with no issue or template; PR titles
  are conventional without an issue ref; ADR/PRD files use the PR number
- CONTEXT.md: drop the PR-template predicates (k328, templates-mandatory)

scripts/release-notes/conventional-title.cjs

@@ -3,15 +3,11 @@
 /**
  * Single source of truth for conventional-commit PR-title parsing.
  *
- * Consumed by BOTH:
- *   - the release-notes changelog classifier
- *     (scripts/release-notes/format-github-release-notes.cjs), and
- *   - the PR-title CI gate (.github/workflows/pr-title-validator.yml, via
- *     evaluatePrTitle).
- *
- * Keeping one matcher here is the point of #1549: a forked copy of the regex
- * would let the gate accept a title that the changelog then mis-buckets. Both
- * the bucket anchors and the gate must read the title the same way.
+ * Consumed by the release-notes changelog classifier
+ * (scripts/release-notes/format-github-release-notes.cjs). `evaluatePrTitle`
+ * backed the upstream PR-title CI gate (#1549), which MSD does not run; it is
+ * kept so a title can still be checked against the same matcher the
+ * changelog buckets on.
  */
 
 // Bucket anchors. The leading `^` is load-bearing: the changelog buckets on the