chore: remover skills e prompts do OpenSpec de .github

[andrenfe]

Remove .github/skills/ e .github/prompts/ (OpenSpec), que estavam sendo captados pelo npx skills add nfe/client-nodejs e misturados com a skill do SDK. Mantidos workflows e copilot-instructions.md. Sem mudança de versão.

[github-actions]

📋 OpenAPI Spec Validation

✅ All specs validated and types generated successfully

Specs processed:

• calculo-impostos-v1.yaml - 27.90 KB, 853 lines
• consulta-cnpj.yaml - 34.28 KB, 1128 lines
• consulta-cpf.yaml - 3.39 KB, 83 lines
• consulta-cte-v2.yaml - 18.33 KB, 578 lines
• consulta-endereco.yaml - 11.17 KB, 343 lines
• consulta-nf-consumidor.yaml - 43.41 KB, 1279 lines
• consulta-nf.yaml - 137.87 KB, 3119 lines
• consulta-nfe-distribuicao-v1.yaml - 53.07 KB, 1775 lines
• nf-consumidor-v2.yaml - 293.87 KB, 7609 lines
• nf-produto-v2.yaml - 309.41 KB, 8204 lines
• nf-servico-v1.yaml - 257.42 KB, 6252 lines
• nfeio.yaml - 15.86 KB, 630 lines

Generated types available as artifact in src/generated/.