Behaviour and tiny DSL for executable Vibe skills.
Executable skills are trusted local .exs files that combine Markdown guidance
with callable Elixir helpers. They can expose eval APIs through
Vibe.Plugin.API without becoming long-running plugins.
Summary
Types
Callbacks
@callback apis() :: [Vibe.Plugin.API.t() | keyword() | map()]
@callback markdown() :: String.t()
@callback metadata() :: metadata()