fix: use correct API to invoke Copilot code review in doc-review workflow

[Copilot]

The copilot-review job was calling gh pr edit --add-reviewer "copilot-reviews" — a command that silently succeeds but never triggers GitHub Copilot code review. Separately, the visual review comment used @copilot, which is not a valid Copilot handle in PR comments.

Changes

• copilot-review job: Replace shell command with actions/github-script calling pulls.requestReviewers with copilot-pull-request-reviewer — the correct reviewer identifier for Copilot code review. Adds graceful error handling that surfaces a link to the repository ruleset config if the API call fails.

  - name: Request Copilot review
    uses: actions/github-script@...
    with:
      script: |
        await github.rest.pulls.requestReviewers({
          owner: context.repo.owner,
          repo: context.repo.repo,
          pull_number: prNumber,
          reviewers: ['copilot-pull-request-reviewer'],
        });

• copilot-visual-review job: Replace @copilot with @github-copilot, the correct handle for invoking Copilot in PR/issue comments.

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