docs: drop soak + 2-week-pilot as PR 7.2 preconditions

The parity matrix gate is the precondition for retiring the legacy
Galaxy projects. The 24h × 50k soak run and 2-week production pilot
were sketched in early planning as additional safety nets but aren't
operationally applicable for this deployment — there's no separate
production fleet to pilot against, and the soak harness's value is as
ongoing diagnostic infrastructure (still shipped in PR 6.4) rather
than a one-shot release gate.

PR 7.2's only remaining precondition is the matrix being fully green
or carrying documented accepted-deltas — verified 2026-04-30 on the
dev rig: 14 passed / 1 skipped / 0 failed.

Affected:
- docs/v2/Galaxy.ParityMatrix.md "Outstanding deltas" — flips to
  "PR 7.2 is unblocked"
- docs/v2/Galaxy.ParityRig.md "After the rig is green" — drops the
  three-step soak+pilot flow, keeps only the matrix-doc bookkeeping
  follow-up
- lmx_mxgw_impl.md PR 7.2 "Depends on" — replaces "fully soaked"
  with the matrix-green precondition + the verification date

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/v2/Galaxy.ParityMatrix.md

@@ -124,8 +124,8 @@ suite skips or tolerates them by design.
 ## Outstanding deltas
 
 None as of 2026-04-30. Phase 7 (PR 7.1) flipped the default to
-`mxgw`; PR 7.2 retires the legacy projects after the soak run + a
-2-week production pilot.
+`mxgw`; PR 7.2 (legacy project deletion) is unblocked — the matrix
+gate is satisfied and no further soak/pilot precondition applies.
 
 ## Running the matrix