feat: add folding provider contract catalog

[intel352]

Summary

• adds a public FoldingProviderContract catalog constructor for workflow-compute
• exposes the protocol aliases needed by consumers without retyping core contracts
• validates the Folding contract identity and warm-service runtime envelope

TDD

• red: TestFoldingProviderContract_DocumentsWarmServiceRuntime failed before the constructor and protocol aliases existed
• green: implemented the catalog constructor and upgraded workflow-plugin-compute-core to the protocol version that defines the shared runtime constants

Verification

• GOWORK=off go test ./internal -run 'TestFoldingProviderContract_DocumentsWarmServiceRuntime|TestFoldingUpstreamClientRequirement_DocumentsImagePolicy' -count=1
• GOWORK=off go test ./... -count=1
• git diff --check