Feature request: Auto-detect TTY for --output default across all deadline CLI commands

[crowecawcaw]

Describe the problem

The deadline CLI has seven subcommands that accept an --output flag (job wait, job logs, bundle submit, bundle gui-submit, bundle run, auth status, config show). They all default to a human-readable format (verbose or text).

This is the right default for a human at a terminal, but the wrong default for the two largest non-human audiences:

1. AI agents and scripts invoking the CLI to parse its output. They have to remember to pass --output json on every call, or build a wrapper.
2. Pipelines and redirection like deadline job logs --job-id … > out.txt, where the human writer is no longer the reader.

The current situation also forces agent-oriented docs and tools to repeat --output json everywhere, which is boilerplate that the CLI should handle itself.

Proposed Solution

When --output is not specified, detect whether stdout is a TTY and default to json when it is not. Humans at a terminal keep today's human-readable output; agents, pipes, and CI get JSON automatically. Explicit --output values always win.

Prior art for this pattern:

• AWS CLI switches its pager and output behavior based on whether stdout is a terminal. See Using the AWS CLI pager and the cli_auto_prompt / output configuration.
• kubectl drives color and table-vs-machine output off TTY detection via its IOStreams abstraction and documents the machine-output shift in kubectl get output formats.

Example Use Cases

Agent invocation becomes boilerplate-free.

Before:

deadline bundle run ./my_bundle --output json -q
deadline job logs --job-id "$JOB_ID" --output json
deadline job wait --job-id "$JOB_ID" --output json

After:

deadline bundle run ./my_bundle
deadline job logs --job-id "$JOB_ID"
deadline job wait --job-id "$JOB_ID"

Humans keep the readable output with no change. Running any of these commands in a terminal still prints the human format.

CI or container jobs without a TTY get JSON for free:

- name: Wait for job
  run: deadline job wait --job-id ${{ steps.submit.outputs.job-id }}

Opt-out for edge cases. A script that wants human output despite being non-interactive can pass --output verbose; a human who wants JSON in a terminal can pass --output json.