Split Docker Compose into base/dev/prod/traefik overrides with multi-instance support

- Split docker-compose.yml into base config + environment overrides
  - docker-compose.dev.yml: port mappings for local development
  - docker-compose.prod.yml: external proxy-net network, no exposed ports
  - docker-compose.traefik.yml: optional Traefik auto-discovery labels
- Parameterize container and volume names with COMPOSE_PROJECT_NAME
  - Default: hub-dev (containers: hub-dev-api, volumes: hub-dev_hub_data)
  - Override per instance for multi-instance deployments (hub-prod, hub-beta)
- Add Makefile with build/up/down/logs/backup/restore targets
- Add TRAEFIK_DOMAIN env var for Traefik routing configuration
- Update UPGRADING.md with volume migration instructions (rename + copy methods)
- Update README.md with multi-instance deployment and backup/restore sections

docker-compose.dev.yml

@@ -0,0 +1,28 @@
+# MeshCore Hub - Development Docker Compose Override
+#
+# Exposes service ports for local development and testing.
+# NOT intended for production use — use docker-compose.prod.yml instead.
+#
+# Usage:
+#   docker compose -f docker-compose.yml -f docker-compose.dev.yml up -d
+
+services:
+  mqtt:
+    ports:
+      - "${MQTT_PORT:-1883}:${MQTT_PORT:-1883}"
+
+  api:
+    ports:
+      - "${API_PORT:-8000}:8000"
+
+  web:
+    ports:
+      - "${WEB_PORT:-8080}:8080"
+
+  prometheus:
+    ports:
+      - "${PROMETHEUS_PORT:-9090}:9090"
+
+  alertmanager:
+    ports:
+      - "${ALERTMANAGER_PORT:-9093}:9093"