fix(infra): check out shell scripts with LF

On Windows git converted infra/postgres/init.sh to CRLF; Postgres then failed to run it
(/bin/bash^M: bad interpreter), so the identity/clinical databases and roles were never
created and every API call returned 500.

Refs #77

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

.gitattributes

@@ -0,0 +1,2 @@
+# Shell scripts run inside Linux containers: never check them out with CRLF (bash fails on the carriage return).
+*.sh text eol=lf