enh: Smarter primary service detection in multi-service compose files

[nfebe]

Context

From PR #109 review.

pickPrimaryService returns the first service with ports/expose in multi-service compose files. In Go maps, iteration order is random, so the selected service may not be the intended primary.

Location

internal/docker/discovery.go — pickPrimaryService()

Suggested improvement

Prioritize services named app or web before falling back to the first with ports:

for name, svc := range services {
    if (name == "app" || name == "web") && (len(svc.Ports) > 0 || len(svc.Expose) > 0) {
        return name, svc
    }
}
for name, svc := range services {
    if len(svc.Ports) > 0 || len(svc.Expose) > 0 {
        return name, svc
    }
}