fix(memory-core): keep reflection running when park.json is unreadable

A truncated or foreign runtime/reflection/park.json threw out of
ReflectionReservationStore.tryReserve, so a corrupt breaker record blocked
every reservation, manual /reflect included. The store now reads an
unreadable file as the empty park state (only ReflectionParkStateError and
SyntaxError are tolerated; I/O errors still propagate), /doctor keeps
reporting the file through the strict reader, and the next park transition
rewrites it.

The park record moves into park-file.ts (ReflectionParkFile: read, write,
transition) so reservation.ts drops from 287 to 233 pure LOC. park.test.ts
pins the 3 / 6 / 6 h thresholds by equality.

Part of #8304