docs: clarify fields and jq usage

[leet-c1]

Summary

• Prefer --fields for known JSON keys in read output.
• Define jq-only cases: conditional selection, reshaping, aggregation, sorting, and mutation-result extraction.
• Surface the rule in README, embedded agent guidance, CLI help, and changelog.

Validation

• go test ./...
• go vet ./...
• golangci-lint run --timeout=3m ./...
• Live: users list --fields id,email and a jq conditional pipeline against the lab tenant.