feat: use compute-core catalog protocol

[intel352]

Summary

• switch compute.provider_catalog validation to github.com/GoCodeAlone/workflow-plugin-compute-core/protocol.ProviderContract
• declare workflow-plugin-compute-core as a plugin dependency
• update catalog tests/docs/spec to describe the public protocol boundary while leaving runtime dispatch APIs on workflow-compute

Verification

• GOWORK=off go test ./internal -run 'ProviderCatalog|ModuleSchemas|PluginManifestModuleTypes' -count=1
• GOWORK=off go test ./... -v -race -count=1
• GOWORK=off go build ./...
• GOWORK=off go vet ./...
• git diff --check
• (workflow) GOWORK=off go run ./cmd/wfctl plugin validate-contract /Users/jon/workspace/workflow-plugin-compute