chore: add .gitattributes for consistent line endings

Ensures shell scripts keep LF and PowerShell scripts keep CRLF across
Windows and Linux checkouts.

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

.gitattributes

@@ -0,0 +1,21 @@
+# Auto-detect text files and normalize line endings to LF in the repo
+* text=auto eol=lf
+
+# Scripts must keep their platform-native line endings
+*.sh text eol=lf
+*.ps1 text eol=crlf
+
+# Documentation and config
+*.md text eol=lf
+*.json text eol=lf
+*.yml text eol=lf
+*.yaml text eol=lf
+*.toml text eol=lf
+*.tsv text eol=lf
+
+# Never let Git touch line endings in these
+*.png binary
+*.jpg binary
+*.jpeg binary
+*.gif binary
+*.ico binary