Add pgAdmin to the peo4c image

Install pgAdmin 9.18 in its own virtualenv and run it under gunicorn on
port 5050 next to PostgreSQL and the bridge. On first start the
entrypoint creates the pgAdmin login (PGADMIN_DEFAULT_EMAIL, default
admin@example.com; PGADMIN_DEFAULT_PASSWORD, default POSTGRES_PASSWORD)
and registers the bundled PostgreSQL server. pgAdmin is optional
(PEO4C_PGADMIN=false) and a failure in it does not stop the container.

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

Dockerfile

@@ -3,9 +3,10 @@
 # Stage 1 builds the neo4j-browser static frontend from source.
 # Stage 2 is the Apache AGE image (PostgreSQL with the AGE extension) plus the
 # peo4c bridge, which speaks the Bolt protocol to the browser and translates
-# Cypher into AGE `cypher()` calls.
+# Cypher into AGE `cypher()` calls, and pgAdmin as a SQL interface.
 
 ARG AGE_IMAGE=docker.io/apache/age:release_PG18_1.8.0
+ARG PGADMIN_VERSION=9.18
 
 FROM docker.io/library/node:16.20.2-bullseye AS browser
 
@@ -23,13 +24,23 @@ RUN yarn build && test -f dist/index.html
 
 FROM ${AGE_IMAGE}
 
+ARG PGADMIN_VERSION
+
 RUN apt-get update \
-    && apt-get install -y --no-install-recommends python3 python3-psycopg \
+    && apt-get install -y --no-install-recommends python3 python3-psycopg python3-venv \
     && rm -rf /var/lib/apt/lists/*
 
+RUN python3 -m venv /opt/pgadmin \
+    && /opt/pgadmin/bin/pip install --no-cache-dir "pgadmin4==${PGADMIN_VERSION}" gunicorn \
+    && ln -s "$(/opt/pgadmin/bin/python -c 'import sysconfig; print(sysconfig.get_paths()["purelib"])')/pgadmin4" \
+        /opt/pgadmin/app \
+    && mkdir -p /var/lib/pgadmin \
+    && chown postgres:postgres /var/lib/pgadmin
+
 COPY --from=browser /src/dist /opt/peo4c/browser
 COPY bridge /opt/peo4c/bridge
 COPY docker/initdb/ /docker-entrypoint-initdb.d/
+COPY docker/pgadmin/config_distro.py /opt/peo4c/pgadmin/config_distro.py
 COPY docker/peo4c-entrypoint.sh /usr/local/bin/peo4c-entrypoint.sh
 
 ENV PEO4C_DEFAULT_GRAPH=neo4j \
@@ -37,10 +48,13 @@ ENV PEO4C_DEFAULT_GRAPH=neo4j \
     PEO4C_HTTP_PORT=7474 \
     PEO4C_BOLT_PORT=7687 \
     PEO4C_PG_HOST=127.0.0.1 \
-    PEO4C_PG_PORT=5432
+    PEO4C_PG_PORT=5432 \
+    PEO4C_PGADMIN=true \
+    PEO4C_PGADMIN_PORT=5050 \
+    CONFIG_DISTRO_FILE_PATH=/opt/peo4c/pgadmin/config_distro.py
 
-# 7474: neo4j-browser (HTTP), 7687: Bolt, 5432: PostgreSQL
-EXPOSE 7474 7687 5432
+# 7474: neo4j-browser (HTTP), 7687: Bolt, 5050: pgAdmin, 5432: PostgreSQL
+EXPOSE 7474 7687 5050 5432
 
 ENTRYPOINT ["/usr/local/bin/peo4c-entrypoint.sh"]
 CMD ["postgres", "-c", "shared_preload_libraries=age"]