Phase 544: whiteboard primitive persistence schema policy gate

[ExplodingUFO]

Summary

• record the Phase 544 whiteboard primitive persistence schema policy gate in both parity roadmap locales
• add WHITEBOARD_PRIMITIVE_PERSISTENCE_SCHEMA_POLICY_GATE coverage for schema-version, migration, workspace, clipboard, and screenshot boundaries
• keep the slice docs/tests-only with no runtime/API/schema/renderer/screenshot-manifest behavior changes

Verification

• dotnet test tests\AsterGraph.Demo.Tests\AsterGraph.Demo.Tests.csproj -c Release --filter "FullyQualifiedName~ReactFlowParityRoadmapDocsTests.ParityRoadmapDocs_RecordPhase544WhiteboardPrimitivePersistenceSchemaPolicyGateInBothLocales" --verbosity minimal
• dotnet test tests\AsterGraph.Demo.Tests\AsterGraph.Demo.Tests.csproj -c Release --filter "FullyQualifiedName~ReactFlowParityRoadmapDocsTests" --verbosity minimal
• dotnet test tests\AsterGraph.Demo.Tests\AsterGraph.Demo.Tests.csproj -c Release --verbosity minimal
• git diff --check (LF-to-CRLF warnings only)

Closes #208