Compose passthrough environment variables (${VAR:-}) import as empty string and clobber project-level env vars

[chbndrhnns]

Summary

When a Docker Compose file defines environment variables using standard fallback/passthrough syntax (such as MY_VAR: ${MY_VAR:-} or MY_VAR: ${MY_VAR}), Openship imports this into the service's environment definition with an empty string value ("").

At container runtime, service-level environment variables take precedence over project-level environment variables. Because the service table holds MY_VAR: "", it overrides any non-empty value configured in the Project Settings with an empty string.

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Steps to Reproduce

1. In a compose file (docker-compose.yml), configure a service with a passthrough environment variable:

   services:
     web:
       image: my-image:latest
       environment:
         CONFIG_PARAM: ${CONFIG_PARAM:-}

2. In Openship Project Settings, add CONFIG_PARAM=my-production-value.
3. Deploy the project.
4. Inspect the running container environment (printenv CONFIG_PARAM inside the container).

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Expected Behavior

The container should receive CONFIG_PARAM=my-production-value from the project environment variables.

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Actual Behavior

The container receives CONFIG_PARAM="" (empty string) because the service-level imported spec sets CONFIG_PARAM: "", which clobbers the project-level environment variable.

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Suggested Resolution

• When importing compose environment variables, do not store unpopulated placeholder fallbacks as explicit service-level overrides.
• Alternatively, during compose parsing, interpolate project-level environment variables into ${VAR} references, or treat empty service-level defaults as fallback to project-level variables during the merge step.