- Update util.go: 1.64.1 -> 1.87.0 (nixpkgs version for devbox services)
- Update flakeref test: v0.40.2 -> v1.87.0 (GitHub tag)
- Remove unused processComposeTargetVersion constant from devbox.go
- Update postgresql plugin to use foreground mode instead of daemon mode
  (required for compatibility with process-compose 1.75.0+)

The postgresql plugin change:
- Changed from `pg_ctl start` with `is_daemon: true` to running `postgres`
  directly with `is_daemon: false`
- This is the recommended pattern for process managers and fixes
  compatibility with newer process-compose versions

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>