feat: GraphQL presentation skill

[joao-oliveira-softtor]

Track

Presentation & transport — see ROADMAP

Goal

Skill for GraphQL resolvers as presentation adapters:

• validation at the edge (equivalent to request DTOs)
• handlers/use cases unchanged
• no domain leakage

Acceptance

• SKILL.md + references (resolver patterns, validation)
• Agent optional or route via presentation-agent
• Tiny example mutation/query against an existing BC pattern
• Architecture checklist respected