test: cover service ps pretty output

[Bortlesboat]

Related to #201

- What I did

Added coverage for the default docker service ps table output, corresponding
to the remaining pretty-print item in #201.

- How I did it

The test drives the command with a fake service and representative task, uses
--no-resolve, and checks stable headings and identifying row values without
depending on volatile elapsed-time output.

AI assistance: OpenAI Codex helped draft the test. I reviewed the complete diff
and validation evidence and take responsibility for the contribution.

- How to verify it

Run the focused TestServicePsPrettyPrint test in ./cli/command/service.
gofmt -d cli/command/service/ps_test.go and git diff --check are clean.

On this Windows checkout, the broader package run still has the existing
LF/CRLF golden-output failures in TestServiceContextWrite, TestPrettyPrint,
and TestServiceListOrder; the new test passes.

- Human readable description for the release notes

- A picture of a cute animal (not mandatory but encouraged)