Projektdateien hinzufügen.

NET48_BUILD.md

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+# .NET Framework 4.8 build
+
+The IMSApiDotNet library now multi-targets:
+
+- `netstandard2.0`
+- `net48`
+
+## Visual Studio
+
+Open `IMSApiDotNet_10.0.0-59_HttpClient.sln` and select **Build > Rebuild Solution**.
+
+The library outputs are:
+
+- `src\IMSApiDotNet\bin\Release\netstandard2.0\IMSApiDotNet.dll`
+- `src\IMSApiDotNet\bin\Release\net48\IMSApiDotNet.dll`
+
+For a classic .NET Framework 4.8 application, reference the DLL from the `net48` folder.
+
+## Command line
+
+Build only the .NET Framework 4.8 variant:
+
+```powershell
+.\scripts\build-net48.ps1
+```
+
+or:
+
+```cmd
+scripts\build-net48.cmd
+```
+
+The `Microsoft.NETFramework.ReferenceAssemblies.net48` package is included as a private build dependency. This permits SDK-style `net48` builds even when the .NET Framework 4.8 Developer Pack is not installed locally, provided NuGet restore is available.
+
+The protocol-vector test application remains `net7.0`. This does not affect use of `IMSApiDotNet.dll` from .NET Framework 4.8.