introduce the agent skills standard for packaging reusable instructions that agents can discover and activate at runtime.
- skills defined via SKILL.md with yaml frontmatter and markdown body
- three-level progressive disclosure: metadata, instructions, resources
- filesystem discovery with directory name validation
- skill lifecycle events (discovery, loaded, activated, failed)
- crew-level skills resolved once and shared across agents
- skill context injected into both task execution and standalone kickoff
