chore: reorganize project and add test project

YKanBan.Tests/YKanBan.Tests.csproj

@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="MSTest" Version="4.4.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\YKanBan\YKanBan.csproj" />
+  </ItemGroup>
+
+</Project>