Add npm test script and example validation test against meta-schema

[BelfordZ]

Motivation

• Ensure every JSON example in src/examples is valid against the repository's src/meta-schema.json by adding a test that exercises every example.
• Provide a standard way to run tests via an npm test script so CI and contributors can validate examples easily.

Description

• Added a test npm script ("test": "node --test") to package.json to run the Node test runner.
• Added dev dependencies ajv and ajv-formats and recorded changes to package-lock.json to support JSON Schema validation in tests.
• Introduced test/examples-meta-schema.test.mjs, a Node test which loads src/meta-schema.json, discovers each *.json file in src/examples, and validates each example with Ajv, failing with readable errors if validation fails.
• Made validation deterministic/offline-friendly by registering the draft-07 meta-schema under the https://meta.json-schema.tools (with and without trailing slash) reference and enabling formats via ajv-formats.

Testing

• Ran npm install to install added dev dependencies, which completed successfully.
• Ran npm test during development; initial run failed due to Ajv attempting to fetch the external meta-schema, which led to a fix mapping https://meta.json-schema.tools to the bundled draft-07 schema.
• After the fix, npm test succeeded and the suite reported all validations passing (all example files in src/examples validated successfully).

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Codex Task