Feature: --json output format for machine-readable output

[erdemtuna]

Source: codeFindings.md Section 6 (Medium Priority)

Machine-readable output for CI pipelines and tooling integration. At minimum for list, outdated, tree, and validate.

$ craft list --json
[{"alias":"company-standards","version":"2.1.0","url":"github.com/org/standards","skills":["api-conventions","error-formats"]}]

$ craft outdated --json
[{"alias":"company-standards","current":"2.1.0","latest":"2.2.0","type":"minor"}]

Could use --json flag or --format json pattern (like gh CLI).