Run Explorer compatibility checks in CI

[marpaia]

Summary

This adds the CI layer for evaluating sbol-db as SynBioHub's Explorer-compatible search backend.

• Run the indexed /search/I0462 HTML contract on every push for Virtuoso with SBOLExplorer, sbol-db with SBOLExplorer, and sbol-db in both roles.
• Run the complete pinned SBOLTestSuite corpus weekly and on manual dispatch against the SBOLExplorer baseline and the sbol-db candidate on separate runners.
• Retain the backend reports, comparison report, and Compose logs as workflow artifacts.

Staging

This is a stacked draft based on marpaia/sbol-db-and-explorer. Until the companion synbiohub-docker PR merges, both workflows intentionally check out marpaia/sbol-db-and-explorer from that repository. The Docker ref should be changed to snapshot before this PR is marked ready for merge.

Validation

• actionlint for both changed workflows
• YAML parsing for both changed workflows
• 4 conformance harness unit tests
• Compose configuration for the SBOLExplorer and native sbol-db topologies
• Isolated live smoke runs for both search backends: every substantive gate passed, and all four smoke probes had identical submissions, counts, first pages, and ordering

Smoke mode intentionally leaves the full-corpus gate false; the scheduled/manual workflow is the exhaustive 291-document gate.