Validate compose project name before using it in docker-compose command lines

[carfeii]

Fixes #828.

Summary

The auto-detected local project name, and any explicit Service/Project
ProjectName, can originate from the com.docker.compose.project Docker
label. Unlike a project name declared via docker-compose.yml, a raw
container label has no format restriction: docker run --label accepts
any string, including one containing extra command-line flags. That value
was concatenated unescaped into the docker-compose command prefix used to
build every generated command (restart, stop, logs, etc.), allowing
argument injection from any container on the host whose
com.docker.compose.service label happened to match one of the project's
service names.

Fix

Adds isValidComposeProjectName, matching the character class the Compose
spec itself requires for a project name, and uses it in two places:

• RefreshContainersAndServices: a container's ProjectName label is
  skipped during auto-detection if it doesn't pass validation, so the
  loop continues to a legitimate match instead of adopting it.
• NewCommandObject: the -p flag is only appended if the project name
  passes validation, as defense in depth in case an invalid value reaches
  this point through another path.

Testing

• go build ./... and go test ./... pass with no changes to existing
  test expectations.
• Manually reproduced the injection against an unpatched checkout (crafted
  a container with a com.docker.compose.project label containing
  --project-directory, matching service name web) and confirmed the
  resolved RestartService command's argv contained the injected flag.
  Repeated the same setup against this branch and confirmed the label is
  now rejected, detection falls through to the legitimate project name,
  and the resolved command's argv is unaffected by the malicious
  container's label.

Happy to add an automated regression test for this in pkg/commands if
you'd like one included, following the existing test style in that
package. I kept this PR to the minimal fix in the meantime.