Add full JSON output and clear command feedback

Scripts and agents driving the CLI needed every command to speak JSON, and several commands used to succeed without printing anything.

• Added --json output to whoami, link, unlink and service status, and made API command errors return structured JSON instead of plain text
• Added success messages to all create, update and delete commands (Created part <id>) so they no longer succeed silently
• Fixed environment bootstrap output corrupting the --json event stream during runs