Check text files out with LF on every platform

The Windows runner checks out CRLF by default, so the formatter rejected every
source file and the job never reached the tests. Also marks the test documents
binary so git can never rewrite bytes the engine inspects.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: Garfield-yin

.gitattributes

@@ -0,0 +1,15 @@
+# Check every text file out with LF, on every platform. Without this a Windows
+# checkout gets CRLF and the formatter rejects the whole tree.
+* text=auto eol=lf
+
+# Test documents are inspected byte for byte; never let git rewrite them.
+*.pdf binary
+*.doc binary
+*.docx binary
+*.xls binary
+*.xlsx binary
+*.ppt binary
+*.pptx binary
+*.key binary
+*.numbers binary
+*.pages binary