Bulk-update API-origin skills. Always a bulk operation: send an items array
(1–100 items). Each item is resolved by its /skill/source +
/skill/externalId locator and must include at least one writable field.
Updates apply only to skills created via this public API; a locator that points
to a non-API-origin skill is reported as not found.

/skill/proficiencyLevels is a full replacement when supplied. Per-item results
are returned in results; the request returns 200 even when some items fail.

Rate limit: 10 requests/min per tenant.

OAuth scope (app-user): job_catalog.skills:write.

IAM permission: Job catalog / Skills / Manage (company-scoped).