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)

.github/PULL_REQUEST_TEMPLATE/fix.md

@@ -1,74 +0,0 @@
-## Fix PR
-
-> **Using the wrong template?**
-> — Enhancement: use [enhancement.md](?template=enhancement.md)
-> — Feature: use [feature.md](?template=feature.md)
-
----
-
-## Linked Issue
-
-> **Required.** This PR will be auto-closed if no valid issue link is found.
-
-Fixes #
-
-> The linked issue must have the `confirmed-bug` label. If it doesn't, ask a maintainer to confirm the bug before continuing.
-
----
-
-## What was broken
-
-<!-- One or two sentences. What was the incorrect behavior? -->
-
-## What this fix does
-
-<!-- One or two sentences. How does this fix the broken behavior? -->
-
-## Root cause
-
-<!-- Brief explanation of why the bug existed. Skip for trivial typo/doc fixes. -->
-
-## Testing
-
-### How I verified the fix
-
-<!-- Describe manual steps or point to the automated test that proves this is fixed. -->
-
-### Regression test added?
-
-- [ ] Yes — added a test that would have caught this bug
-- [ ] No — explain why: <!-- e.g., environment-specific, non-deterministic -->
-
-### Platforms tested
-
-- [ ] macOS
-- [ ] Windows (including backslash path handling)
-- [ ] Linux
-- [ ] N/A (not platform-specific)
-
-### Runtimes tested
-
-- [ ] Claude Code
-- [ ] Antigravity
-- [ ] OpenCode
-- [ ] Other: ___
-- [ ] N/A (not runtime-specific)
-
----
-
-## Checklist
-
-- [ ] Issue linked above with `Fixes #NNN` — **PR will be auto-closed if missing**
-- [ ] Linked issue has the `confirmed-bug` label
-- [ ] Fix is scoped to the reported bug — no unrelated changes included
-- [ ] Regression test added (or explained why not)
-- [ ] All existing tests pass (`npm test`)
-- [ ] `.changeset/` fragment added if this is a user-facing fix (`npm run changeset -- --type Fixed --pr <NNN> --body "..."`) — or `no-changelog` label applied
-- [ ] No unnecessary dependencies added
-
-## Breaking changes
-
-<!-- Does this fix change any existing behavior, output format, or API that users might depend on?
-     If yes, describe. Write "None" if not applicable. -->
-
-None