feat: make JSON output consistent across the CLI

[rmanibus]

Summary

Add a consistent global -json output mode across Cloudstic CLI commands so machine-readable output is predictable and documented.

Scope

• add a shared global -json flag
• make supported commands emit structured JSON when requested
• keep human-readable output unchanged when -json is not used
• update help text, completion, tests, and docs to match the behavior

Notes

This is intended to improve scripting, automation, and parity across commands without changing the client API.

Related

• PR feat: add consistent JSON output across the CLI #185