print commit hash on import; fix event_id offset in multi-core steps

G4Calo.py prints the commit at import time, resolved via a
minicalo_version.py file (baked in by Docker) or git rev-parse
from the file's directory as fallback.

event_id in the Steps ntuple restarts from 0 in each subprocess;
_assemble_results_to_mini_df now accepts per-file event_id_offsets
so IDs are globally unique after merging. run_batch passes cumulative
nevents as offsets when loading the Steps tree.

Dockerfiles write minicalo_version.py before copying Python files.

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

docker/Dockerfile-mini

@@ -52,9 +52,11 @@ RUN cd /root/minicalosim && git checkout $COMMIT && \
     cmake --build build --parallel $(nproc) && \
     cp build/minicalo*.so /usr/local/lib/python3.10/dist-packages/
 
-RUN cp /root/minicalosim/bind/G4Calo.py \
+RUN echo "commit = '${COMMIT}'" > /root/minicalosim/bind/minicalo_version.py && \
+    cp /root/minicalosim/bind/G4Calo.py \
        /root/minicalosim/bind/minicalo_tools.py \
        /root/minicalosim/bind/minipandas.py \
+       /root/minicalosim/bind/minicalo_version.py \
        /usr/local/lib/python3.10/dist-packages/ && \
     install -m 755 /root/minicalosim/bind/G4Calo_exec.py /usr/local/bin/G4Calo_exec.py