Enforce docs wiki publication in build-docs workflow

[Copilot]

build-docs could succeed without publishing docs, or fail late with an opaque wiki clone error. This change makes wiki publication an explicit requirement of the job and surfaces a clear failure when wiki sync is not possible.

• Workflow contract hardening

  • Added an explicit wiki availability gate before sync.
  • The job now fails early if ${repo}.wiki.git is unreachable, instead of silently skipping publication.

• Auth behavior

  • Wiki operations now use token fallback: secrets.WIKI_ACTION_TOKEN || github.token.
  • Keeps sync operable with repo-level token defaults while still honoring a dedicated wiki token when configured.

• Wiki action wiring

  • Uses supported github-wiki-action@v4 inputs for path and commit message.
  • Sync step is now part of the required publish path rather than optional behavior.

- name: Verify wiki repository availability
  env:
    GH_TOKEN: ${{ secrets.WIKI_ACTION_TOKEN || github.token }}
  run: |
    if ! git ls-remote "https://x-access-token:${GH_TOKEN}@github.com/${{ github.repository }}.wiki.git" HEAD >/dev/null 2>&1; then
      echo "::error::GitHub wiki repository is unavailable. Enable the repository wiki and ensure token permissions allow wiki push."
      exit 1
    fi

- name: Sync Wiki
  uses: Andrew-Chen-Wang/github-wiki-action@v4
  with:
    token: ${{ secrets.WIKI_ACTION_TOKEN || github.token }}
    path: docs/api
    commit-message: "docs: update API documentation [skip ci]"