Bulk create workspaces

Create up to 100 workspaces in one request. Each item runs the full single-item flow independently — parent resolution, the depth cap, the access relationships and the member projection — so a failed item that grants nothing also creates nothing.

Partial success: always 207 Multi-Status, one slot per index. Items may name different parents, and the create receipt is checked per distinct parent.

A batch may not name a workspace created earlier in the same batch as a parent: parents are resolved from a read set taken once, before the first item, so a just-created sibling is not in it. That is deliberate rather than incidental — the alternative is a batch whose meaning depends on item order.