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>

docs/v1/README.md

@@ -0,0 +1,30 @@
+# v1 documentation archive
+
+This folder contains documentation that described the original v1
+in-process MXAccess architecture (`Galaxy.Host` + `Galaxy.Proxy` +
+`Galaxy.Shared` three-project split, .NET 4.8 x86 + COM apartment, the
+`OtOpcUaGalaxyHost` Windows service). That architecture was retired in
+PR 7.2 (merged 2026-04-30 at commit `ae7106d`). These docs are kept as
+the historical record of how the system worked before the v2-mxgw
+migration; treat their content as accurate at the time of writing, NOT
+as current state.
+
+For current architecture see:
+
+- `CLAUDE.md` — agent-facing v2 overview
+- `docs/drivers/Galaxy.md` — current Galaxy driver doc
+- `docs/v2/Galaxy.ParityRig.md` — current testing setup
+- `docs/v2/Galaxy.Performance.md` — observability + perf
+- `lmx_mxgw.md` (in repo root) — design rationale for the migration
+
+| File | What it covered |
+|---|---|
+| `AlarmTracking.md` | v1 alarm-tracking flow through the in-process MXAccess client |
+| `Configuration.md` | v1 server configuration (`OTOPCUA_GALAXY_*` env vars now live in mxaccessgw config) |
+| `DataTypeMapping.md` | Galaxy `mx_data_type` → OPC UA type mapping (still accurate as a reference; the live mapping logic is in `src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/Browse/DataTypeMap.cs`) |
+| `HistoricalDataAccess.md` | v1 IHistoryProvider on the Host side; current path is the server-level HistoryRouter + Wonderware sidecar |
+| `Subscriptions.md` | v1 MXAccess subscription mechanics; current path uses gateway StreamEvents |
+| `drivers/Galaxy-Repository.md` | v1 Host-side ZB SQL repository client; the gateway owns this path now |
+| `drivers/Galaxy-Test-Fixture.md` | v1 test-fixture setup (parity tests + Galaxy.Host EXE spawn) |
+| `reqs/GalaxyRepositoryReqs.md`, `reqs/MxAccessClientReqs.md` | Original Phase 0 requirements; satisfied in mxaccessgw repo today |
+| `reqs/ServiceHostReqs.md` | Service-hosting requirements including `OtOpcUaGalaxyHost` (GHX-* section); only `OtOpcUa` server hosting remains in scope post-7.2 |