feat(deploy): enable single-domain routing for one click deployment

[sivasubramanian95]

Summary

This PR enables single-domain deployment for Flowrabbit (one-click platform friendly) by switching default routing to path-based rules, while preserving optional legacy host-based compatibility
through an override compose file.

Problem

The previous setup depended on multiple subdomains (api.*, studio.*, proxy.*, apps.*, docs.*) and host-based Traefik routing, which makes one-click deployments difficult.

What Changed

• Updated default docker-compose.yaml to single-domain path routing:
  • / -> studio
  • /apps -> apps
  • /docs -> docs
• Added FLR_PUBLIC_URL-based URL composition.
• Updated app-side URL defaults to support path-based mode.
• Added docker-compose.local.yaml for localhost override.
• Added docker-compose.legacy-hosts.yaml for optional host-based compatibility mode.
• Added .env.example and required env-based secrets in compose.
• Switched persistent data to named volumes for better cross-platform stability.
• Updated README deployment instructions.

Validation

• docker compose config passes for:
  • default mode
  • local override mode
  • legacy-host override mode
• Local smoke test (Windows):
  • http://localhost/ -> 200
  • http://localhost/api/rest/status.json -> 200
  • http://localhost/docs/status.json -> 200
  • http://localhost/apps -> 200

Compatibility / Notes

• Single-domain is now the default mode.
• Legacy subdomain routing is still available via:
  • docker compose -f docker-compose.yaml -f docker-compose.legacy-hosts.yaml up -d