chore: pin LF line endings for shell scripts, nginx/compose configs, Dockerfiles

install.sh is copied from the Windows dev machine to Linux client boxes; with
core.autocrlf=true a fresh checkout would give it CRLF endings and bash would
fail on it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitattributes

@@ -0,0 +1,7 @@
+# Files that run or are read on Linux client machines must keep LF endings,
+# even when checked out on Windows with core.autocrlf=true (install.sh is scp'd as-is).
+*.sh        text eol=lf
+*.conf      text eol=lf
+Dockerfile  text eol=lf
+*.yml       text eol=lf
+.env.example text eol=lf