Improve CLI human output base

[odyslam]

Supersedes the closed oversized PR #90. This is stack slice 1/8.

Base: main
Head: codex/pcl-human-output-base

What changed:

• Establishes the base human-output UX layer for the CLI.
• Keeps TOON/JSON envelopes as the machine contract while making default output more useful for people.
• Adds coverage around the output behavior introduced by this base slice.

Review focus:

• CLI output contract boundaries: human output should not bleed into --toon or --json.
• New output helpers and tests in the changed CLI/core files.

Validation:

• make ci passed on the stack tip codex/pcl-slim-generated-client.
• Local ./target/debug/pcl smoke passed for --toon --llms, doctor --toon, auth ensure --toon, whoami --toon, workflows --toon, schema list --toon, and api manifest --toon.

[odyslam]

Superseded by #96, which now combines the human-output base and polish slices as review step 1/5.