Pin .cs working-tree line endings to CRLF

.gitattributes marked *.cs as `text` with no `eol=`, so the checked-out line
ending was left to each machine's git config. On the CI runner the .cs come out
LF, but .editorconfig sets end_of_line=crlf, so dotnet-format's --verify-no-changes
flagged every line of every file and the Format check step failed repo-wide
(independent of code formatting). Pinning eol=crlf makes the checkout match the
editorconfig on every platform. Blobs stay LF; only the working-tree EOL is fixed.

Assisted-by: Claude:claude-opus-4-8:Claude Code

.gitattributes

@@ -1,4 +1,4 @@
 * text=auto
-*.cs text diff=csharp
+*.cs text eol=crlf diff=csharp
 *.sln text eol=crlf
 *.csproj text eol=crlf