docs: correct cached credit help text

[emecii]

ade help parse --json and ade help extract --json said that credits is zero on a cached hit. The CLI actually returns the original run's bill for both fresh and cached results, which lets callers retain the cost associated with the job item.

Correct the generated help contract and its checked-in JSON reference to describe that behavior. No API or stored data changes.

Validation:

• 23 help and help-style tests pass.
• Full offline suite: 742 passed, eight skipped; one unrelated existing shipping test fails because a deterministic telemetry-content hash differs between two requests. This wording-only change does not affect telemetry or shipping code.
• The project does not install Ruff in its development dependency group, so its configured lint command could not be invoked locally.

Implemented and checked with OpenAI Codex (GPT-6).