Behavior: Creates "related content" links between content items as specified in the list. Related content represents semantic relationships between items (e.g., "see also", "part of series"). Returns a batch result with per-item status.

Authorization: Requires a valid Bearer token.

Side Effects: Creates related content association records.

Error Scenarios: Returns 400 if the input is null or the items list is empty. Returns 404 if the items list is null.