net8.0: upgrade from netcoreapp3.1, fix Linux rendering

- TFM: netcoreapp3.1 → net8.0, netstandard2.1 → net8.0
- System.Drawing.Common 5.0.3 → 6.0.0 (last version with Unix support)
- Remove stale packages (NETStandard.Library, System.Collections)
- Set System.Drawing.EnableUnixSupport via runtimeconfig + AppContext
- Pin System.Resources.Extensions 8.0.0, suppress NU1603
- Copy game_folder assets to build output (no run.sh required)
- Sta.CurrentDirectory → AppContext.BaseDirectory for portable path resolution
- Enable UnsafeBinaryFormatterSerialization + InvariantGlobalization
- Add global.json pinning SDK to 8.x
- Remove ambiguous `using System.Net.Mime.MediaTypeNames` in ParT.cs
- Add `using System.Reflection` to Program.cs

SlaveMatrix/SlaveMatrix.csproj

@@ -4,7 +4,7 @@
     <AssemblyName>SlaveMatrix</AssemblyName>
     <GenerateAssemblyInfo>False</GenerateAssemblyInfo>
     <OutputType>WinExe</OutputType>
-    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <PlatformTarget>x64</PlatformTarget>
   </PropertyGroup>
   <PropertyGroup>
@@ -14,10 +14,17 @@
   <PropertyGroup>
     <ApplicationIcon>app.ico</ApplicationIcon>
     <RootNamespace />
+    <InvariantGlobalization>true</InvariantGlobalization>
+    <EnableUnsafeBinaryFormatterSerialization>true</EnableUnsafeBinaryFormatterSerialization>
+    <SuppressTfmSupportBuildWarnings>true</SuppressTfmSupportBuildWarnings>
+    <NoWarn>CA1416</NoWarn>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\2DGAMELIB\2DGAMELIB.csproj" />
   </ItemGroup>
+  <ItemGroup>
+    <Content Include="..\game_folder\**\*" CopyToOutputDirectory="PreserveNewest" LinkBase="" />
+  </ItemGroup>
   <ItemGroup>
     <Compile Update="Properties\Resources.Designer.cs">
       <DesignTime>True</DesignTime>