build: manage version via MinVer with AssemblyInformationalVersion

Uses MinVer to derive the version from git tags (prefix "v"), stored in
AssemblyInformationalVersion. Program.cs reads that attribute (stripping
the "+sha" build metadata) so the update-check compares against a clean
semver. CI overrides the tag via /p:MinVerVersionOverride=$VERSION.

Directory.Build.props

@@ -0,0 +1,8 @@
+<Project>
+  <PropertyGroup>
+    <MinVerTagPrefix>v</MinVerTagPrefix>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="MinVer" Version="5.0.0" PrivateAssets="all" />
+  </ItemGroup>
+</Project>