Add compute core protocol

[intel352]

Summary

• instantiate public workflow-plugin-compute-core from the plugin scaffold
• add public compute provider catalog protocol types, validation helpers, and canonical hashing
• strip scaffold/runtime capability placeholders so this plugin acts as a dependency anchor

Verification

• GOWORK=off go build ./...
• GOWORK=off go test ./... -v -race -count=1
• GOWORK=off go vet ./...
• GOWORK=off go run ./cmd/wfctl plugin validate-contract /Users/jon/workspace/workflow-plugin-compute-core (from /Users/jon/workspace/workflow)
• git diff --check