List every available Ripostiq course (no login needed). Call this FIRST when a user wants
to browse or start learning. Each course has a free Module 1 anyone can start immediately via
begin_course(course) → teach_section. Returns the `course` id to pass to other tools.
For a logged-in learner this also includes courses THEY authored (marked `mine`, with their
`visibility`) — offer those alongside the catalog.
ConnectorNo auth