docs(engines): template on shared services and a determinism rule

New engines start from the shared test kit (the template's tests are a
one-line EngineContractTests subclass) and the host APIs, so they don't
re-derive geometry reading, work areas or validator tolerances.
BENCH-RULES.md now forbids clocks, unseeded randomness and environment
variables from influencing placement (budgets count work; wall time only
through the host's cancellation token) and lists the kit as read-only.
Build-Engines.ps1 deploys only OpenNest.Engine.* folders, and
New-Engine.ps1 -IncludeBuildFiles copies the kit.

Co-Authored-By: Codex <noreply@openai.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Build-Engines.ps1

@@ -27,7 +27,7 @@ if (-not (Test-Path (Join-Path $OpenNestRoot 'OpenNest.Benchmark/OpenNest.Benchm
 }
 $OpenNestRoot = (Resolve-Path $OpenNestRoot).Path
 
-dotnet build (Join-Path $OpenNestRoot 'OpenNest.Benchmark/OpenNest.Benchmark.csproj') -c $Configuration
+dotnet build (Join-Path $OpenNestRoot 'OpenNest.Benchmark/OpenNest.Benchmark.csproj') -c $Configuration -m:1 -nr:false
 if ($LASTEXITCODE -ne 0) { throw 'OpenNest.Benchmark build failed.' }
 
 $deployDir = Join-Path $OpenNestRoot "OpenNest.Benchmark/bin/$Configuration/net8.0/Engines"
@@ -38,7 +38,7 @@ $projects = Get-ChildItem $PSScriptRoot -Directory -Filter 'OpenNest.Engine.*' |
 
 foreach ($dir in $projects) {
     $csproj = Join-Path $dir.FullName "$($dir.Name).csproj"
-    dotnet build $csproj -c $Configuration "-p:OpenNestRoot=$OpenNestRoot/"
+    dotnet build $csproj -c $Configuration "-p:OpenNestRoot=$OpenNestRoot/" -m:1 -nr:false
     if ($LASTEXITCODE -ne 0) { throw "$($dir.Name) build failed." }
 
     $dll = Join-Path $dir.FullName "bin/$Configuration/net8.0/$($dir.Name).dll"