fix(entrypoint): drop dash-incompatible ERR trap

CI logged only "trap: ERR: bad trap" — /bin/sh is dash, which rejects ERR
traps and then set -e exits before hostname checks or /data setup. Keep
portable step() echoes for the next CI diagnosis.

Co-Authored-By: Composer <noreply@cursor.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

build/entrypoint.sh

@@ -7,9 +7,8 @@
 # tests see the FATAL text rather than an earlier set -e abort).
 set -e
 # #region agent log
-# Debug: CI showed exit=1 with empty docker logs after /data/opendkim was
-# created — surface the failing line under set -e (session 816647).
-trap 'echo "entrypoint: command failed at line $LINENO (exit $?)" >&2' ERR
+# Debug (session 816647): dash does not support `trap … ERR` ("bad trap" then
+# set -e aborts before hostname checks). Step echoes only — portable on /bin/sh.
 step() { echo "entrypoint: $*" >&2; }
 # #endregion