Use synbiohub-docker snapshot in CI

[marpaia]

Summary:

• point the integration and search-conformance workflows at the maintained synbiohub-docker snapshot branch
• consume the v0.1.3 sbol-db defaults merged in Update sbol-db to v0.1.3 synbiohub-docker#28
• remove the stale dependency on the deleted marpaia/sbol-db-and-explorer branch

This addresses both failure modes in master run 30647783848: the Explorer matrix can check out its Docker topology again, and the store-only sbol-db job reruns against v0.1.3 with literal SPARQL as the default behavior.

Local validation:

• python3 -m unittest tests/search-backends/test_run_conformance.py tests/search-backends/test_compare_reports.py
• git diff --check

The decisive gate is this PR's full Integration testing workflow.