Add explicit GITHUB_TOKEN permissions to workflows

[dduugg]

Resolves the four open actions/missing-workflow-permissions CodeQL
alerts. Each scope is the least privilege the job actually needs:

• build.yml (chore(deps): bump terser from 5.13.1 to 5.14.2 #5): workflow-level contents: read. The single build
  job only checks out, restores an actions/cache entry, and runs
  npm ci / npm run build:prod / npm test. Neither setup-node nor
  actions/cache needs a token scope beyond reading the repo.
• publish.yml (Add team Slack CTA #1): workflow-level contents: read. Despite the name,
  this tag-triggered job does not publish anything — it runs
  vsce package and hands the .vsix to actions/upload-artifact.
  Uploading an artifact needs no extra scope, there is no
  vsce publish, no gh release create, and no npm publish, so no
  write scope is warranted. The Marketplace release is done off the
  artifact, not by this token.
• stale.yml (Prepare for publishing #2): job-level issues: write + pull-requests: write.
  The shared-config stale workflow runs actions/stale, which comments
  on and closes both stale issues and stale PRs. A caller's permissions
  are the ceiling for the reusable workflow, so both scopes must be
  granted here or the nightly cron silently stops closing things.
• triage.yml (Fix last reference to bigrails #4): job-level issues: write. The shared-config triage
  workflow only runs gh issue edit --add-label triage.

Callers use job-level blocks immediately above uses:, matching the
accepted precedent in rubyatscale/query_packwerk. codeql.yml already
declares its permissions and is left untouched.

Alerts resolved

• #5 actions/missing-workflow-permissions (medium) — .github/workflows/build.yml:11
• #4 actions/missing-workflow-permissions (medium) — .github/workflows/triage.yml:9
• #2 actions/missing-workflow-permissions (medium) — .github/workflows/stale.yml:8
• #1 actions/missing-workflow-permissions (medium) — .github/workflows/publish.yml:8

Verification

• Every job in every flagged workflow now has an effective permissions: block (cross-checked by parsing the YAML against the alert list).
• actionlint output is byte-identical to main — no new findings introduced.
• codeql.yml untouched.