feat: add vmss command slice

[TacoRocket]

Summary

• add the vmss compute command with schema, fixture, help, table, and golden coverage
• retire the selected sort-order debt for dns, api-mgmt, and keyvault
• tighten acronym/help wording and align fixture-backed VMSS workload surfaces across commands

Validation

• python3 -m ruff check src tests scripts
• PYTHONPATH=src python3 -m pytest -o cache_dir=/private/tmp/pytest-cache-all