Build a CLI tool to validate and add new API previews

[akuligowski9]

Adding a new API preview currently requires manually creating a JSON file and knowing the correct format. A CLI tool would make this much more accessible for contributors.

Proposed solution
A Node.js CLI script (extending the existing scripts/generate-previews.cjs) that:

1. Accepts an API name or slug as input
2. Fetches a sample response from the API
3. Auto-detects the best preview type
4. Writes the preview JSON file
5. Validates the output builds correctly

Usage example

node scripts/add-preview.cjs --api "cat-facts"

Acceptance criteria

• Works for APIs in catalog.json
• Validates the generated preview renders without errors
• Handles auth-required APIs gracefully with a prompt for the key