refactor(operator-trend): collapse persistence builders onto a parametrized base (T3-2 phase 6)

The rebuild and rererestore persistence builders were ~190-line hand-clones of one
algorithm -- proven identical by the phase-4 composer golden, the floor fix (#80),
and a differential test over the net's corpus. Extract a single
_persistence_for_target_base plus a _PersistenceTierSpec carrying the per-tier
literals (status keys, status tokens, reason prose, output keys); both public
builders become thin wrappers that pass their spec.

Public signatures are unchanged, so the apply-chain wiring, the rerererestore
delegation wrapper (which injects the rererestore builder), and all other callers
are untouched.

Net -121 lines (265 insertions, 386 deletions). The composer golden is
byte-identical -- a correct collapse changes no output -- and the full suite (2539
passed) is green. Correctness is demonstrated, not assumed.

Author: saagpatel