[Docs]: Document structured SIST results

[harryswift01]

Documentation Update

Document how to generate, understand, validate, and reuse structured SIST result files.

Why Is This Needed?

Users need to understand the result fields, units, indexing, metadata, warnings, and schema versions before they can safely use the JSON output.

Suggested Changes

Document:

• How to enable JSON output.
• The structure of a result file.
• Important fields and units.
• Array shapes and indexing.
• Metadata and warnings.
• Missing and invalid values.
• Schema compatibility.
• Loading and validating saved results.
• Basic downstream-analysis examples.

Include a minimal and a representative complete example.

Done When

• Users can generate and load a result using the documentation.
• Important fields, units, and indexing are explained.
• Warnings and incomplete runs are covered.
• Schema compatibility is explained.
• Analysis without rerunning SIST is demonstrated.