feat(simulator): web data-plane explorer

Single-page view over the Parquet lake: live partition tree with
rolled-up sizes and a SQL console gated by the same read-only rules
as the peer query channel. Ships in the monitoring profile.

simulator/docker-compose.yml

@@ -31,6 +31,18 @@ services:
     ports:
       - "${EXPORTER_PORT:-9105}:9105"
 
+  explorer:
+    build: .
+    profiles: [monitoring]
+    command: ["python", "explorer/server.py"]
+    environment:
+      DATA_DIR: /data
+    volumes:
+      - ./data:/data:ro
+      - ./explorer:/app/explorer:ro
+    ports:
+      - "${EXPLORER_UI_PORT:-8088}:8088"
+
   prometheus:
     image: prom/prometheus:v2.53.0
     profiles: [monitoring]