Sakila execute-tier fixture for the Jakarta ValidationHandler channel (R94-blocked)

Split out from R12 (error-handling-parity)'s "Test fixture updates for source-direct dispatch" bullet. R12 lifted ValidationHandler channel support and the Jakarta pre-execution validation step into the per-fetcher catch path. Execute-tier coverage is blocked on R94 (emit-input-records): the pre-step today calls validator.validate(env.getArgument(name)), which receives a Map<?, ?> (or a raw scalar); neither carries Jakarta annotations, so the validator returns no violations and the wire path is a no-op end-to-end. R94 emits each SDL input type as a graphitron-internal Java record under <outputPackage>.inputs, coerces the map at the fetcher boundary, and gives the validator a real annotated bean to inspect; once R94 lands this fixture becomes a one-line addition to the sakila execute-tier driver.

Scope: an @service mutation whose input declares Jakarta constraints, an @error type with {handler: VALIDATION}, and an execute-tier driver covering the violation path (constraint produces a typed error via ConstraintViolations.toGraphQLError) and the happy path. Pipeline-tier coverage of the emit shape is already pinned in TypeFetcherGeneratorTest and FetcherPipelineTest.