Feature: Add JSON Output Mode

[chefgs]

Title

Add --json flag to CLI commands

Why

Many users may want to integrate DevOps-OS into automation pipelines.

Example:

python -m cli.devopsos scaffold gha --json

Instead of printing text, return structured JSON.

Example output:

{
  "workflow": ".github/workflows/my-app.yml",
  "type": "github_actions"
}