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/TeslaLauncherAgent.cs

@@ -422,8 +422,8 @@ namespace Tesla.Launcher.Agent
             }
 
             var resBytes = Encoding.UTF8.GetBytes(JsonSerializer.Serialize(response));
-            pipe.Write(BitConverter.GetBytes(resBytes.Length));
-            pipe.Write(resBytes);
+            pipe.Write(BitConverter.GetBytes(resBytes.Length), 0, 4);
+            pipe.Write(resBytes, 0, resBytes.Length);
             pipe.Flush();
         }
 
@@ -672,7 +672,7 @@ namespace Tesla.Launcher.Agent
             var scalar = parms[0].ValueKind == JsonValueKind.Number
                 ? (float)parms[0].GetDouble()
                 : throw new Exception("Invalid volume value");
-            SetMasterVolume(Math.Clamp(scalar, 0f, 1f));
+            SetMasterVolume(Math.Max(0f, Math.Min(1f, scalar)));
             return null;
         }