Set up `oxa` CLI NPM package

[nokome]

Set up the main OXA CLI npm package for validating documents against the schema. Create packages/oxa/ with:

package.json

• Package name: oxa
• Binary: oxa
• Dependencies: oxa-types (workspace), commander, ajv, ajv-formats, js-yaml

src/cli.ts

• Main CLI entry point using commander
• validate command that validates JSON/YAML files against the OXA schema
• Support for stdin input
• Exit codes: 0 for valid, 1 for invalid, 2 for errors

src/index.ts

• Export validation utilities for programmatic use
• Re-export types from oxa-types

Tasks

• Create packages/oxa/package.json with bin entry
• Create packages/oxa/tsconfig.json
• Implement packages/oxa/src/cli.ts with validate command
• Implement packages/oxa/src/index.ts with exports
• Add build script to compile TypeScript
• Test CLI validation against sample documents

[rowanc1]

Regarding:

Re-export types from oxa-types

In the node-clis that I have created recently, I have made them dependency-free and just have the bin file. That means that download is really fast on a npm install -g oxa, but anything else comes from a different package (e.g. @oxa/cli or similar for reuse of the functions etc.).