Add .gitattributes to enforce LF line endings (#158)

No CRLF files exist in the repository. Add .gitattributes with
`* text=auto eol=lf` to prevent CRLF from being introduced going forward,
consistent with the .editorconfig policy.

Co-authored-by: Claude <noreply@anthropic.com>

Author: bernardladenthin

.gitattributes

@@ -0,0 +1,5 @@
+# SPDX-FileCopyrightText: 2026 Bernard Ladenthin <bernard.ladenthin@gmail.com>
+#
+# SPDX-License-Identifier: MIT
+
+* text=auto eol=lf