Add .gitattributes: force LF line endings for shell scripts

Without this, git on macOS with core.autocrlf=true checks out .sh
files with CRLF. Bash then reads 'CONTAINER_NAME\r' as the variable
name (never set), causing 'unbound variable' with set -u.

https://claude.ai/code/session_01FKCW3FDjNFj6jve4niMFXH

.gitattributes

@@ -0,0 +1,14 @@
+# Force LF line endings for shell scripts on all platforms.
+# Without this, git on macOS/Windows with core.autocrlf=true checks out
+# .sh files with CRLF, which causes bash to read variable names as
+# "VARNAME\r" and fail with "unbound variable" errors.
+*.sh    text eol=lf
+
+# Other text files — normalise to LF in the repo.
+*.rs    text eol=lf
+*.toml  text eol=lf
+*.md    text eol=lf
+*.yml   text eol=lf
+*.yaml  text eol=lf
+*.env*  text eol=lf
+Caddyfile text eol=lf