Discover the config's variable surface (viewer)

Parses the staged config (terragrunt render + variables.tf, or plain tofu) and returns every module variable with its configured state. The default field carries the value the config resolves — a terragrunt input or a module default — so it is only populated for callers who clear the variable-management bar (admin, or an admin team grant on this workspace). Below that bar the response is names, types, descriptions and provenance with no values, and the terragrunt render that would resolve them is skipped. Synchronous; intentionally not list-enveloped.