Rename peo4c to peo

Renames the Python package, environment variables (PEO4C_* to PEO_*), the
SQL helper schema, image paths and the entrypoint script.

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

docker/initdb/10-peo.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 # SPDX-FileCopyrightText: 2026 Bart Broere
 # SPDX-License-Identifier: GPL-3.0-or-later
-# Prepares a freshly initialised cluster for peo4c.
+# Prepares a freshly initialised cluster for peo.
 set -euo pipefail
 
 # The bridge connects over 127.0.0.1 with the credentials users log in with, so
@@ -12,7 +12,7 @@ sed -i -E 's/^(host[[:space:]]+[^[:space:]]+[[:space:]]+[^[:space:]]+[[:space:]]
 
 # Create the default AGE graph that neo4j-browser opens on first connect.
 psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "${POSTGRES_DB:-$POSTGRES_USER}" \
-    -v graph="${PEO4C_DEFAULT_GRAPH:-neo4j}" <<'EOSQL'
+    -v graph="${PEO_DEFAULT_GRAPH:-neo4j}" <<'EOSQL'
 LOAD 'age';
 SET search_path = ag_catalog, "$user", public;
 SELECT ag_catalog.create_graph(:'graph')