Automate parsing of SSSOM Mappings

[M-casado]

Summary

Add a small script and CI step that:

• Parses every meta:sssomMappings block in our FEGA JSON-Schema (schemas/) repo
• Verifies each mapping is syntactically valid SSSOM and that subject_id, predicate_id, object_id resolve (this may be problematic with unresolvable GDI minimal harmonised model, but would be pretty handy for reviews)
• Checks that the cross-standard mappings (e.g., from GDI to FEGA) in the Cardinality section of the technical report (./docs/technical-report.md) are up-to-date (no missing or extra rows)
• Potentially produces an artifact:
  • cardinality-table.md: a condensed Markdown table for the report appendix

Acceptance criteria

• GitHub Action runs on PRs and fails if a mapping is malformed or the report table is stale.
• Script documented in README.md with one-line usage (e.g., in a python script).