Improve error handling in command plugin and CLI

[simplecloud-vercel-github]

Problem

Error handling in the command plugin and CLI should be improved so users receive clear, consistent outcomes when commands cannot be completed.

Expected behavior

Both interfaces should handle errors gracefully and provide actionable error messages and useful diagnostics. Command failures should communicate an appropriate exit or status result.

Acceptance criteria

• Error messages are consistent and actionable across the command plugin and CLI where applicable.
• Failures are handled gracefully without unclear or misleading output.
• Useful diagnostics are available to help users understand a failure.
• Command failures produce appropriate exit or status behavior.
• Successful behavior remains unchanged.