fix(db): restore postgres command dropped by entrypoint override

Overriding entrypoint in compose clears the image default CMD, leaving
pgautoupgrade with no $1=postgres, so its version logic ran with unset
PGTARGET_MAJOR and aborted. Restore command: postgres.

compose.yml

@@ -78,6 +78,9 @@ services:
         target: /pg_backup.sh
         mode: 0555
     entrypoint: /usr/local/bin/cc-db-entrypoint.sh
+    # overriding entrypoint drops the image's default CMD, so restore it; the
+    # wrapper passes "$@" through and pgautoupgrade keys its logic on $1=postgres
+    command: postgres
     environment:
       - POSTGRES_HOST_AUTH_METHOD=trust
       - POSTGRES_USER=discourse