List boards

List all boards belonging to the calling workspace as a flat array, depth-first ordered (parent then its descendants then the next sibling). Reconstruct the tree on the client by following parent_id links — children is always empty on this surface to avoid duplicating the same nodes across the response.

Top-level boards carry parent_id == workspace_id as a sentinel.

Page-based pagination — pass page=2, page=3, ... to walk the list. Each board is returned exactly once across all pages.

Returns: code=0 success; code=40001 workspace context missing.