Create or update multiple links

Create or update up to 1000 links in one request. The body is a JSON array where each item uses the same schema as POST /api/v1/link — include id to update, omit it to create, and provide workspace_id per item (required for API-key auth; ignored for OAuth, whose token is scoped to a single workspace). Returns one result per item and responds 200 even if some items fail — inspect each item's status.