Retrieve a commitment detail read model

Retrieves the detail read model for one Commitment, backing the commitment detail page on route load. The payload bundles the commitment itself (type, term, payment, family, region, status, hourly/upfront/ monthly-savings figures in ten-thousandths of the currency unit, utilization/coverage percentages, effective discount fraction, start/expiry timestamps, days-to-expiry and the covered resources with per-resource coverage and on-demand-equivalent cost) plus the trailing 30-day utilization/coverage timeline with per-day committed and on-demand-equivalent amounts in ten-thousandths of the currency unit. Requested data is returned without mutating the resource. Validation: scopeId must be accessible to the caller and commitmentId must identify a commitment within that scope — an unknown or out-of-scope id maps to 404 NOT_FOUND; no body or other inputs. Async & state: Synchronous read; no state change. Status transitions (QUEUED→ACTIVE, ACTIVE→EXPIRING) and renewals arrive as resource.updated SSE frames of kind billing.commitment with a patch of the changed fields. Errors: 401 unauthenticated; 403 caller lacks a billing-capable role on the scope; 404 unknown scopeId or commitmentId; 500 internal read failure. Idempotency/Concurrency: Safe, cacheable; no idempotency key required. The response carries no ETag; purchase and renew do not check If-Match.