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

.env.example

@@ -29,6 +29,17 @@
 # =============================================================================
 # These settings apply to all services
 
+# Docker Compose project name
+# Used as a prefix for container names (e.g., hub-dev-api) and volume names
+# (e.g., hub-dev_hub_data). Change per instance when running multiple deployments
+# on the same Docker host (e.g., hub-prod, hub-beta, hub-stg).
+# For multi-instance setups, see the "Multi-Instance Deployment" section in README.md.
+COMPOSE_PROJECT_NAME=hub-dev
+
+# Domain name for this instance (only needed for Traefik deployments)
+# Used by docker-compose.traefik.yml to configure routing rules
+# TRAEFIK_DOMAIN=meshcore.example.com
+
 # Docker image version tag to use
 # Options: latest, main, v1.0.0, etc.
 IMAGE_VERSION=latest