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/build.bat

@@ -3,11 +3,12 @@
 :: TeslaLauncher — Unified Build / Package Script
 :: =============================================================================
 :: Publishes TeslaLauncherService.exe and TeslaLauncherAgent.exe as
-:: self-contained single-file win-x64 executables (net8) and assembles the
-:: installable TeslaLauncher\ package next to install.bat.
+:: framework-dependent net48 builds and assembles the installable TeslaLauncher\
+:: package next to install.bat. The target pod needs .NET Framework 4.8 (built
+:: into Windows 10/11) — there is no bundled runtime, so the package is small.
 ::
 :: Requirements:
-::   .NET 8 SDK  https://dotnet.microsoft.com/download/dotnet/8.0
+::   .NET SDK (6.0+) to drive the build  https://dotnet.microsoft.com/download
 ::   Internet access for NuGet restore (first build only)
 ::
 :: Usage:
@@ -31,7 +32,6 @@ setlocal enabledelayedexpansion
 
 set ROOT=%~dp0
 set BUILD_DIR=%ROOT%TeslaLauncher
-set RID=win-x64
 
 :: -- Parse arguments ----------------------------------------------------------
 set BUILD_SERVICE=1
@@ -46,7 +46,7 @@ for %%a in (%*) do (
 
 echo.
 echo ============================================================
-echo  Tesla Launcher v0.1 - Build ^& Package (net8, %RID%)
+echo  Tesla Launcher v0.1 - Build ^& Package (net48, framework-dependent)
 echo  Output : %BUILD_DIR%
 echo ============================================================
 echo.
@@ -75,9 +75,6 @@ echo [1/2] Publishing TeslaLauncherService (Session 0 Windows Service)...
 echo.
 dotnet publish "%ROOT%TeslaLauncherService.csproj" ^
     -c Release ^
-    -r %RID% ^
-    --self-contained true ^
-    -p:PublishSingleFile=true ^
     -o "%BUILD_DIR%\Service"
 if errorlevel 1 (
     echo.
@@ -98,9 +95,6 @@ if %BUILD_SERVICE%==1 (echo [2/2] Publishing TeslaLauncherAgent...) else (echo [
 echo.
 dotnet publish "%ROOT%TeslaLauncherAgent.csproj" ^
     -c Release ^
-    -r %RID% ^
-    --self-contained true ^
-    -p:PublishSingleFile=true ^
     "-p:DefineConstants=WINFORMS" ^
     -o "%BUILD_DIR%\Agent"
 if errorlevel 1 (