Return an AiAkiv guide document for a topic, as text.
Use this when the user asks how to use AiAkiv or MWeft, wants the tutorial,
or pastes an `aiakiv.com/llms-*.txt` link that cannot be opened here. The
result is a reference document to read and draw on, not a set of commands.
Read-only.
Args:
topic: One of `"tour"` (first-run tutorial, llms-tour.txt),
`"playbook"` (projects and personas, llms-playbook.txt), `"setup"`
(install and connect, llms.txt), `"demo"` (public demo-memory
walkthrough, llms-tour-demo.txt), or `"console"` (the console app
actions for teams, links, audit and cards, llms-console.txt). It
defaults to `"tour"`, so a request for one of the other four
carries the topic. Any other value returns an error listing these
five.
Returns:
`{topic, source_url, content, cached, available_topics}` — or
`{error, hint}` when the topic is unknown or the fetch fails.