feat(memory-core): park automatic reflection after repeated failures

ReflectionReservationStore keeps runtime/reflection/park.json under the
scheduler lock. complete() accepts a failure classification, feeds the park
policy for automatic runs, clears it on merged/no_changes, reports the park
edge to the caller and drops an automatic pending promotion when the identity
just parked. evaluate() and tryReserve() refuse automatic requests while
parked (status "parked" with the next probe time) except for the one
half-open probe per interval, which stamps lastProbeAt.

The reservation file helpers move to reservation-files.ts so the store stays
under the file-size ceiling; the existing reservation suite pins that the
extraction changed no behavior.

Part of #8304