Fix: upgrade Java 17→21 for Neo4j 2026.x compatibility

Dockerfile

@@ -27,8 +27,8 @@ ENV LANG=C.UTF-8
 
 # ── System dependencies ────────────────────────────────────────────────────────
 RUN apt-get update && apt-get install -y --no-install-recommends \
-    # Java for Neo4j
-    openjdk-17-jre-headless \
+    # Java for Neo4j 2026.x (requires Java 21+)
+    openjdk-21-jre-headless \
     # Python
     python3.11 python3-pip python3.11-venv \
     # Web / infra

docker/supervisord.conf

@@ -16,7 +16,7 @@ serverurl=unix:///tmp/supervisor.sock
 # ── Neo4j Community ────────────────────────────────────────────────────────────
 [program:neo4j]
 command=/opt/neo4j/bin/neo4j console
-environment=NEO4J_HOME=/opt/neo4j,JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64,NEO4J_CONF=/opt/neo4j/conf
+environment=NEO4J_HOME=/opt/neo4j,JAVA_HOME=/usr/lib/jvm/java-21-openjdk-amd64,NEO4J_CONF=/opt/neo4j/conf
 autostart=true
 autorestart=true
 startsecs=45