docs: post-PR-7.2 cleanup — audit + three-track scrub

Audit (three parallel agent passes) found 43 markdown files carrying
stale references to the deleted Galaxy.Host/Proxy/Shared projects
after the v2-mxgw merge. This commit lands the prioritized fixes.

Track 1 — high-traffic in-place rewrites (3 files, ~454 lines deleted)
- README.md (202 → 91 lines): drops .NET 4.8 / x86 / TopShelf install
  text; leads with the multi-driver .NET 10 server identity and points
  at scripts/install/Install-Services.ps1 and the parity rig.
- docs/v2/driver-specs.md §1 Galaxy (~289 → ~66 lines): replaces the
  Tier-C out-of-process spec with a Tier-A in-process description
  matching the current GalaxyDriver code, with the four-section
  GalaxyDriverOptions JSON shape pulled verbatim from
  Config/GalaxyDriverOptions.cs.
- docs/drivers/Galaxy.md (211 → 92 lines): full rewrite around the
  current Browse/Runtime/Health/Config sub-folders.

Track 2 — historical banners (5 files)
- lmx_mxgw.md, lmx_mxgw_impl.md, lmx_backend.md,
  docs/v2/Galaxy.ParityMatrix.md,
  docs/v2/implementation/phase-2-galaxy-out-of-process.md each get a
  "✅ Completed 2026-04-30 — historical record" banner block. lmx_mxgw.md
  also fixes two dead links (`docs/Galaxy.Driver.md` and
  `docs/v2/Galaxy.Driver.md`) → `docs/drivers/Galaxy.md`.

Track 3 — v1 archive sweep (10 git mv + 1 new index + 2 in-place scrubs)
- Moved 10 v1 docs under docs/v1/ preserving subpath structure:
  AlarmTracking, Configuration, DataTypeMapping, HistoricalDataAccess,
  Subscriptions (top-level); drivers/Galaxy-Repository,
  drivers/Galaxy-Test-Fixture; reqs/GalaxyRepositoryReqs,
  reqs/MxAccessClientReqs, reqs/ServiceHostReqs.
- New docs/v1/README.md is the shared archive banner + per-file table.
- docs/README.md repointed to the v1 paths and updated to reflect the
  v2 two-process deploy shape (Server + Admin + optional
  OtOpcUaWonderwareHistorian).
- docs/v2/Galaxy.ParityRig.md got a historical banner + four inline
  scrubs marking the OtOpcUaGalaxyHost service / Driver.Galaxy.Host
  EXE / Driver.Galaxy.ParityTests project as deleted-in-PR-7.2.

The repo's live-reading surface (README + CLAUDE.md + docs/v2/) now
describes only the post-PR-7.2 architecture. v1 docs are preserved as
a labelled archive under docs/v1/.

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

lmx_mxgw_impl.md

@@ -1,3 +1,13 @@
+> **✅ Completed 2026-04-30 — historical record of the v2-mxgw implementation plan.**
+>
+> All 39 PRs across 7 phases (1.1–1.3 + 2.1–2.3 + 1+2.W + 3.1–3.W +
+> 4.0–4.W + 5.1–5.W + 6.1–6.W + 7.1–7.3) shipped and merged to master
+> at commit `ae7106d`. Per-phase status tracking below is preserved as
+> the historical PR-execution log; phase descriptions are
+> retrospective, not pending. Parity matrix verified green on the dev
+> rig 2026-04-30 (14 passed / 1 skipped / 0 failed —
+> see `docs/v2/Galaxy.ParityMatrix.md`).
+
 # Galaxy → MxGateway Migration — Detailed Implementation Plan
 
 Companion to `lmx_mxgw.md` (design plan). This document breaks the plan into