Agent Skills: document-architecture

Generate a high-level architecture document for a module, service, or codebase using 4 parallel Explore sub-agents (data, API/interface, business logic, integrations). Composes with `draw-mermaid-diagram` and `draw-infra-diagram` to embed validated diagrams. Use when asked to "document this codebase", "write architecture docs", "create an arch doc", "generate onboarding docs", "document this service", "map this module". Output is a single Markdown file optimized for human onboarding, not LLM context.