Add DAR JSON schema and validator update

[KristopherKubicki]

Summary

• add dar.schema.json describing DAR file structure
• integrate jsonschema-based checking in dar_validator.py
• document validation steps in new guide and link from README

Testing

• PYTHONPATH=. pytest -q
• python -m py_compile tools/validators/dar_validator.py

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https://chatgpt.com/codex/tasks/task_e_684080a071388333b312075649f81533

[Copilot]

Pull Request Overview

This PR enhances DAR file validation by introducing a JSON schema and integrating jsonschema-based validation into dar_validator.py. Key changes include:

• Adding dar.schema.json to define the DAR file structure.
• Updating DARValidator to accept an optional schema path and perform schema validation.
• Adding documentation in docs/validation.md and updating the README.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tools/validators/dar_validator.py	Updated to use jsonschema for validation and support an optional schema path.
docs/validation.md	New documentation outlining how to validate DAR files.
dar.schema.json	New JSON Schema file defining the DAR file structure.
README.md	Updated to include a link to the validation guide.