feat(scripting): ScriptWorker isolation on Windows: restricted worker identity, pipe ACL, firewall + PeCacheDir installer (lmxopcua#780)

Owner decisions §14 #5/#6 as built (design §12.5):

- Scripting:Worker:Identity (default unset, Windows only, fail-closed validation): each worker
  starts under a restricted token derived from the host's. Every privilege but SeChangeNotify is
  removed; the restricting SIDs are NT SERVICE\OtOpcUaScriptWorker's SID + Everyone + Users +
  RESTRICTED; the token and default DACLs are host + SYSTEM + identity + RESTRICTED. The worker
  is created suspended, put in its Job Object before it runs, inherits only its stdio pipes, gets
  an ACL'd work dir as TEMP, and runs with DOTNET_EnableDiagnostics=0. The identity is granted on
  the host's window station and desktop, because USER32 init made coreclr.dll fail with
  ERROR_DLL_INIT_FAILED on windev. The logon SID is not used because the host's process DACL
  gives it PROCESS_VM_READ.
- The worker pipe on Windows always has an explicit protected DACL: host account + identity
  only. There is no owner ACE, so an elevated host's Administrators gets no access.
- The worker treats access denied on its parent-pid poll as alive; the Job Object covers that case.
- scripts/install/Install-ScriptWorkerIsolation.ps1 + ScriptWorkerIsolation.psm1 are idempotent
  and support -WhatIf, -Uninstall and -PlanOnly. They create the disabled anchor service, the
  PeCacheDir ACL (protected, no Users, key and markers host-only, pe\ Modify for the identity),
  read+execute on script-worker\, a ReadData deny on the install root, the outbound firewall
  block on the worker exe, and optionally the host-service env.
- Tests: the dry-run harness scripts/install/tests/Test-ScriptWorkerIsolation.ps1 (46
  assertions, mutation-checked); ScriptWorkerIdentityTests; WorkerIsolationTests, which cover
  the pipe ACL, token access and a real restricted worker running a script, all green on windev.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

CLAUDE.md

@@ -395,7 +395,7 @@ lists `ScriptedAlarm` — never by default) in `ZB.MOM.WW.OtOpcUa.ScriptWorker`
 (`src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess`, protocol in `Core.Scripting.Protocol`), shipped in `script-worker/`
 beside the host (self-contained + started via its apphost on a `-r win-x64 --self-contained` publish, through the muxer otherwise); a runner-side failure publishes `BadResourceUnavailable` (ScadaBridge-visible, ScadaBridge#112) and the seam re-evaluates
 when the worker is back. `IScriptRunner.RunBatch` sends ready evaluations as one frame per worker (Calc pump, VT coalescer,
-alarm dirty set); a run queued behind busy worker threads has its deadlines restarted when it starts, so it is never blamed for a sibling. Optional `Scripting:Worker:PeCacheDir` = HMAC'd compiled-PE cache (restart without Roslyn); the `script-runner`
+alarm dirty set); a run queued behind busy worker threads has its deadlines restarted when it starts, so it is never blamed for a sibling. Optional `Scripting:Worker:PeCacheDir` = HMAC'd compiled-PE cache (restart without Roslyn); optional (Windows) `Scripting:Worker:Identity` = `NT SERVICE\OtOpcUaScriptWorker` runs workers under a restricted token, set up by `scripts/install/Install-ScriptWorkerIsolation.ps1` (ACLs + outbound firewall block; `docs/ServiceHosting.md`); the `script-runner`
 readiness check is at worst Degraded (never fails ready). The worker tests
 are `tests/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests` (`Category=ScriptWorker`, real processes; `Category=Perf` harness opt-in via
 `OTOPCUA_SCRIPT_PERF=1`). docker-dev overlay: `docker-dev/docker-compose.script-runner.yml`. See `docs/VirtualTags.md`