Add AI-SBOM 1.0.0 validation support

[VinnyBarton]

Summary

Adds support for validating AI-SBOM documents using the AI BOM 1.0.0 schema.

Changes

• Added embedded AI-SBOM 1.0.0 schema under schemas/ai-bom/
• Added AI-SBOM type detection using metadata.bomFormat and AI-SBOM document shape
• Added AI-SBOM version extraction from top-level schemaVersion
• Added schema loading support for AI-SBOM files
• Added valid AI-SBOM examples:
  • customer-support-ai-sbom.json
  • medical-triage-ai-sbom.json
• Added invalid AI-SBOM examples:
  • missing-required-metadata.json
  • bad-types-and-enums-ai-sbom.json
  • unknown-extra-properties-ai-sbom.json
• Updated tests for detection, schema loading, version extraction, and valid/invalid AI-SBOM validation
• Updated README supported formats and example output
• Confirmed existing CycloneDX and SPDX validation behavior continues to pass

Testing

GOCACHE=/private/tmp/sbom-validator-go-cache go test ./...