deprecate custom validator

[madanucd]

Removed all custom Pydantic-based CLI validators previously located in data_validation/. We are now using the standard linkml-validate tool for validation.

• Deleted legacy CLI validation scripts.
• Updated data_validation/README.md to document usage of linkml-validate.
• Validation is now fully handled using LinkML's native functionality.

Closes #231

[lopierra]

@madanucd is it possible to capture a log with the linkml-validator yet?

[madanucd]

@madanucd is it possible to capture a log with the linkml-validator yet?

Yes! We can capture validation output from linkml-validate by redirecting stdout to a file. Here's an example:

linkml-validate -s src/linkml/include_schema.yaml -C Study src/data/input/study.csv > src/data/output/validation-report.md

This allows you to save the validation report as a .md, .txt, .csv, or .json file as needed.

Note: There is also an ongoing effort to customize and improve validation reporting in the BDC, which may offer richer report formats in the future.