Consolidate AWS CLI install and S3 upload into single conditional CI step

[Copilot]

The AWS CLI installation ran unconditionally, wasting CI time even when S3 credentials weren't configured.

Changes

• Merged two steps into one: "Install AWS CLI if missing" and "Upload state/latest to S3" are now a single step
• Early credential check: Step exits immediately if AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_REGION, or CI_LOGS_BUCKET are unset — no installation, no upload attempt
• CI_LOGS_BUCKET via env: Moved from inline ${{ vars.CI_LOGS_BUCKET }} expansion to an env: block alongside the other credentials for consistency

- name: "EXEC: {Install AWS CLI and upload state/latest to S3}, independent"
  if: always()
  env:
    AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
    AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
    AWS_DEFAULT_REGION: ${{ secrets.AWS_REGION }}
    CI_LOGS_BUCKET: ${{ vars.CI_LOGS_BUCKET }}
  run: |
    if [ -z "$AWS_ACCESS_KEY_ID" ] || [ -z "$AWS_SECRET_ACCESS_KEY" ] || [ -z "$AWS_DEFAULT_REGION" ] || [ -z "$CI_LOGS_BUCKET" ]; then
      echo "Skipping S3 upload: AWS credentials or CI_LOGS_BUCKET not configured"
      exit 0
    fi
    # install AWS CLI if needed, then sync to S3

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