add run-at-etp.sh for batch pbwo4 production runs

Builds and runs run_pbwo4 ten times with 10k events each, then moves
the renamed outputs to /ceph/lbogner/geant_steps/.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

run-at-etp.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+cd "$(dirname "${BASH_SOURCE[0]}")"
+
+cmake -B build -S .
+cmake --build build --parallel 8
+
+for i in $(seq 0 9); do
+    build/run_pbwo4 10000
+    mv pbwo4_10000events_hits.root "pbwo4_10k_${i}.root"
+done
+
+mv pbwo4_10k_*.root /ceph/lbogner/geant_steps/