Feature/json cli output

[Yash-choure]

PR TITLE

Add CLI JSON output and fix CI workflow

PR DESCRIPTION

This PR adds a --json option to the scaffold CLI so automation can consume generated file paths and scaffold types. Existing human-readable output remains unchanged.

It also fixes the CI workflow by:

• Updating checkout and artifact actions to supported versions.
• Removing the invalid placeholder GHCR container image.
• Installing Python 3.11, Node.js 20, pytest, PyYAML, and compatible MCP dependencies.
• Using the correct CLI and MCP requirements files.
• Adding GHCR authentication and package permissions.
• Making optional artifact uploads non-fatal.

Validation:

• Workflow YAML parses successfully.
• PyYAML and FastMCP imports pass.
• Pytest collection completes without dependency errors.

Note: A Dockerfile is still required before the deploy job can publish an image to GHCR.

Branch: feature/json-cli-output