Spike: net48-only launcher (evaluate size vs net8 self-contained)

Converts the Launcher Service + Agent from net8/win-x64 self-contained to net48
framework-dependent, and makes Tesla.Contract net48-only (drops multi-targeting).
Both consumers (Console + Launcher) are now a single TFM.

Code changes for net48 (the only net8/netstandard2.1 APIs in use):
- RandomNumberGenerator.Fill -> RandomNumberGenerator.Create().GetBytes (3x)
- TcpListener.AcceptTcpClientAsync(ct) -> AcceptTcpClientAsync() + stop-on-cancel
- byte[].AsSpan().SequenceEqual -> Linq SequenceEqual (no System.Memory) (2x)
- PipeStream.Write(byte[]) / WriteAsync(byte[],ct) -> explicit (buf,0,len[,ct])
- Math.Clamp -> Math.Max/Min
The generic host (Microsoft.Extensions.Hosting 8.x + UseWindowsService) runs on
net48 unchanged. build.bat/install.bat updated for the folder-of-DLLs deploy;
solution platform reverted x64 -> AnyCPU.

RESULT — package size: ~3.7 MB on disk / 1.58 MB zipped, vs ~213 MB / 91 MB for
the net8 self-contained build (~50-58x smaller). net48 ships in Win10/11 so no
runtime prerequisite. 73 tests green; NOT re-validated on a live pod.

Spike branch for evaluation — do not merge without a pod re-test.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Launcher/TeslaLauncherService.csproj

@@ -1,20 +1,17 @@
-<Project Sdk="Microsoft.NET.Sdk.Worker">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0-windows</TargetFramework>
+    <TargetFramework>net48</TargetFramework>
+    <OutputType>Exe</OutputType>
     <Nullable>disable</Nullable>
     <ImplicitUsings>disable</ImplicitUsings>
+    <LangVersion>latest</LangVersion>
     <WarningsAsErrors></WarningsAsErrors>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Version>4.11.4.1</Version>
     <ApplicationIcon>app.ico</ApplicationIcon>
     <AssemblyName>TeslaLauncherService</AssemblyName>
     <RootNamespace>Tesla.Launcher.Service</RootNamespace>
-    <Platforms>x64</Platforms>
-    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
-    <SelfContained>true</SelfContained>
-    <PublishSingleFile>true</PublishSingleFile>
-    <WindowsService>true</WindowsService>
   </PropertyGroup>
 
   <ItemGroup>
@@ -23,22 +20,26 @@
   </ItemGroup>
 
   <ItemGroup>
+    <!-- net48 reference assemblies + GAC refs the framework-dependent build needs. -->
+    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3" PrivateAssets="all" />
+    <Reference Include="System.IO.Compression" />
+    <Reference Include="System.IO.Compression.FileSystem" />
+    <Reference Include="System.ServiceProcess" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <!-- Generic host on .NET Framework: Microsoft.Extensions.Hosting(.WindowsServices)
+         8.x ship a net462 target, so they run on net48 unchanged. -->
     <PackageReference Include="Microsoft.Extensions.Hosting"                  Version="8.*" />
     <PackageReference Include="Microsoft.Extensions.Hosting.WindowsServices"  Version="8.*" />
     <PackageReference Include="Microsoft.Extensions.Logging.EventLog"         Version="8.*" />
-    <!-- Required by SecureConfig.cs for COM2/PlasmaIO serial output -->
+    <PackageReference Include="System.Text.Json"                              Version="8.0.5" />
+    <!-- COM2 / PlasmaIO serial output in SecureConfig.cs -->
     <PackageReference Include="System.IO.Ports"                               Version="8.0.0" />
   </ItemGroup>
 
   <ItemGroup>
-    <!-- Tesla.Net wire types now come from the shared contract (net6 build),
-         replacing the hand-maintained replica in LaunchModels_Shared.cs.
-         SetPlatform pins the reference to AnyCPU: this project is x86, the
-         contract is platform-neutral, and without the pin MSBuild's dynamic
-         platform negotiation corrupts this project's restore (one-shot
-         `dotnet build` of the solution then fails to resolve its packages). -->
-    <ProjectReference Include="..\Contract\Tesla.Contract.csproj" SetPlatform="Platform=AnyCPU" />
+    <ProjectReference Include="..\Contract\Tesla.Contract.csproj" />
   </ItemGroup>
 
-
 </Project>