Smaller automation improvements after Theme Kit 1.2.0

Theme Kit 1.2.0 now covers request timeouts, retries, authentication errors, failed pushes, and NTK_APIKEY. That overlaps with much of #34, so I am closing the draft instead of rebasing the full branch.

A few smaller changes still look useful for CI and agent workflows:

• JSON output for commands such as list, pull, and push, with one stable result on stdout
• options to hide progress bars and routine logs
• a result for each file transferred, including a nonzero exit when only part of a push or pull succeeds
• a core install that does not require libsass unless ntk sass is used

I suggest starting with JSON output and per-file results, then handling packaging separately.

This request does not include hosted screenshots, a new backend endpoint, or changes to the retry and API key work already in 1.2.0. Local theme checks and local screenshots can stay out unless the maintainers want Theme Kit to own them.

Would the team be open to the JSON and per-file work as a first small PR?

Start by reviewing the CLI implementations for list, pull, and push, then inspect the core install requirements and where libsass is declared. Done means stable JSON on stdout, per-file transfer results with a nonzero status for partial failures, and a core install that does not require libsass unless ntk sass is used.