fix: allow ClickHouse connections from Docker network

The default ClickHouse image restricts the 'default' user to localhost
only. Override with clickhouse-users.xml to allow connections from any
IP (needed for inter-container communication on the Docker network).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/clickhouse-users.xml

@@ -0,0 +1,9 @@
+<clickhouse>
+  <users>
+    <default>
+      <networks>
+        <ip>::/0</ip>
+      </networks>
+    </default>
+  </users>
+</clickhouse>