Add .gitattributes: force LF to keep Docker builds working

Git converts to CRLF on checkout under Windows; a CRLF entrypoint or
config file copied into a Linux image fails with "bad interpreter".

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.gitattributes

@@ -0,0 +1,19 @@
+# Keep LF in the repository AND in working copies, on every platform.
+# The Docker images are built from these files on Linux: a CRLF entrypoint,
+# shell script or config silently breaks the build ("bad interpreter").
+* text=auto eol=lf
+
+# Binary assets: never touch.
+*.png binary
+*.jpg binary
+*.jpeg binary
+*.gif binary
+*.ico binary
+*.woff binary
+*.woff2 binary
+*.pdf binary
+
+# Windows-only helpers legitimately keep CRLF.
+*.bat text eol=crlf
+*.cmd text eol=crlf
+*.ps1 text eol=crlf