M1-T06: remove Grafana from compose and delete provisioning

Drop the grafana service and the homeautomation_grafana_storage volume
declaration from docker-compose.yml (migration and app services unchanged),
and delete the grafana/ provisioning + dashboards directory. Visualization
moves to the M2 React frontend; the named volume's actual data is retired
manually as an ops step, never by automation.

docker compose config -q passes; pytest 95 passed; ruff clean.

docker-compose.yml

@@ -25,22 +25,3 @@ services:
       - ./data:/app/data
       - ./.env:/app/.env:ro
 
-  grafana:
-    image: grafana/grafana:latest
-    container_name: home-automation-grafana
-    depends_on:
-      - app
-    restart: unless-stopped
-    ports:
-      - "10.238.75.70:8882:3000"
-    environment:
-      GF_PLUGINS_PREINSTALL: frser-sqlite-datasource
-    volumes:
-      - ./data:/data/home-automation:ro
-      - ./grafana/provisioning:/etc/grafana/provisioning:ro
-      - ./grafana/dashboards:/var/lib/grafana/dashboards:ro
-      - homeautomation_grafana_storage:/var/lib/grafana
-
-volumes:
-  homeautomation_grafana_storage:
-    name: homeautomation_grafana_storage