List stacks for an AI observer

Returns one page of the stacks on a node, projected for an Observe Only token: name, status, running and total container counts, source, and whether the stack is this instance. Stacks are ordered by name; the cursor is the name of the last stack on the previous page, so a stack deleted between two pages does not shift the rest of the list. A directory whose name has characters outside letters, digits, _, and - is not listed, because no per-stack route accepts it. degraded reports that the underlying status evidence was incomplete. This is one of the five paths an Observe Only token may reach. Requires stack:read permission.