fix: allow detach during compose up startup wait

[CyberEclipses]

Fixes #13716

This updates the attached compose up flow so the interactive detach shortcut can interrupt the startup/wait phase.

Previously, the detach shortcut cancelled globalCtx, but service startup was executed with context.WithoutCancel(ctx). As a result, pressing d could cancel the interactive/log side while the startup/wait path continued until services reached running/healthy state.

This change introduces a detach-aware startup context. It keeps startup isolated from parent cancellation for the existing signal-handling behavior, while allowing the explicit detach action to cancel startup/wait and return control cleanly.

Validation:

• gofmt -w pkg/compose/up.go
• go test ./pkg/compose
• go test ./pkg/compose -run Test
• git diff --check
• manual reproduction with a health-gated Compose project:
  • created a project where dependent waits on slow: condition: service_healthy
  • kept slow in healthcheck waiting state
  • ran /tmp/docker-compose -f /tmp/compose-13716-repro/compose.yaml up --menu
  • pressed d while slow was Waiting
  • confirmed the shell prompt returned immediately
  • confirmed slow remained running with docker ps
  • cleaned up with down -v --remove-orphans