Add .gitattributes to normalize line endings to LF

Store and check out LF everywhere (project targets Linux/Docker), ending the LF->CRLF churn warnings on Windows.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitattributes

@@ -0,0 +1,25 @@
+# Normalize line endings: store everything with LF in the repo, and check out
+# LF in the working tree too (this project targets Linux/Docker). Prevents the
+# "LF will be replaced by CRLF" churn on Windows.
+* text=auto eol=lf
+
+# Explicitly text (LF) — source and config.
+*.go     text eol=lf
+*.js     text eol=lf
+*.css    text eol=lf
+*.html   text eol=lf
+*.md     text eol=lf
+*.toml   text eol=lf
+*.yml    text eol=lf
+*.yaml   text eol=lf
+*.mod    text eol=lf
+*.sum    text eol=lf
+Dockerfile text eol=lf
+.env.example text eol=lf
+
+# Treat common binaries as binary (never munge).
+*.png binary
+*.jpg binary
+*.gif binary
+*.ico binary
+*.woff2 binary