chore: enforce least-privilege permissions in GitHub Actions workflows

Set top-level `permissions: {}` on all workflows and move required
permissions to job level. Switch publish.yml from secrets.PAT to
secrets.GITHUB_TOKEN so semantic-release can comment on PRs/issues.

.github/workflows/pr-lint.yml

@@ -6,6 +6,8 @@ on:
   pull_request:
     branches: [master, main]
 
+permissions: {}
+
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true