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>

lmx_mxgw_impl.md

@@ -913,7 +913,9 @@ after 6.4 (uses its data). 6.W last.
   - `Server/Configuration/DriverFactoryRegistry.cs` — remove the
     `legacy-host` switch arm.
 
-**Depends on:** PR 7.1 fully soaked (no rollback risk).
+**Depends on:** parity matrix in `docs/v2/Galaxy.ParityMatrix.md` is
+fully green or carries documented accepted-deltas (verified
+2026-04-30 on the dev rig: 14 passed / 1 skipped / 0 failed).
 
 #### PR 7.3 — Doc + memory housekeeping