chore: enforce LF line endings via .gitattributes

Prettier enforces endOfLine: lf, but core.autocrlf=true was converting
working-copy files to CRLF on checkout, which would flip format:check
red after every branch switch. eol=lf keeps LF in the working tree;
binary assets and Windows scripts are exempted.

.gitattributes

@@ -0,0 +1,22 @@
+# Keep LF in the working copy for all text files (prettier enforces LF)
+* text=auto eol=lf
+
+# Windows scripts that genuinely need CRLF
+*.bat text eol=crlf
+*.cmd text eol=crlf
+*.ps1 text eol=crlf
+
+# Binary assets — never touch line endings
+*.png binary
+*.jpg binary
+*.jpeg binary
+*.webp binary
+*.gif binary
+*.ico binary
+*.icns binary
+*.woff binary
+*.woff2 binary
+*.ttf binary
+*.otf binary
+*.mp4 binary
+*.onnx binary