.github: gate PRs via mitchellh/vouch

Auto-close PRs from authors not listed in .github/VOUCHED.td. Issues
stay open to everyone; the close message points contributors at
CONTRIBUTING.md. Maintainers manage the list with !vouch, !denounce
and !unvouch comments, and a weekly job resyncs CODEOWNERS.

The workflows use GITHUB_TOKEN with explicit least-privilege
permissions.

.github/workflows/vouch-manage-by-issue.yml

@@ -0,0 +1,33 @@
+name: "Vouch - Manage by Issue"
+
+on:
+  issue_comment:
+    types: [created]
+
+permissions:
+  contents: write
+  issues: write
+  pull-requests: write
+
+concurrency:
+  group: vouch-manage
+  cancel-in-progress: false
+
+jobs:
+  manage:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+
+      - uses: mitchellh/vouch/action/manage-by-issue@d66fa29a64600490892131ad87597c30c91fcac4 # v1.5.0
+        with:
+          repo: ${{ github.repository }}
+          issue-id: ${{ github.event.issue.number }}
+          comment-id: ${{ github.event.comment.id }}
+          vouch-keyword: "!vouch"
+          denounce-keyword: "!denounce"
+          unvouch-keyword: "!unvouch"
+          pull-request: "true"
+          merge-immediately: "true"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}