feat: add core placement constraint evaluator

[intel352]

Summary

• Add compute-core placement input DTOs for worker capabilities and task network policy.
• Move placement constraint satisfaction semantics into compute-core without importing workflow-compute's richer worker/task models.

Verification

• RED: GOWORK=off go test ./protocol -run TestPlacementConstraintsSatisfiedByEvaluatesWorkerAndTaskInputs -count=1 failed before implementation with undefined core API symbols.
• GOWORK=off go test ./protocol -run TestPlacementConstraintsSatisfiedByEvaluatesWorkerAndTaskInputs -count=1
• git diff --check
• GOWORK=off go test ./... -count=1

Adversarial Review

• Avoided pulling workflow-compute-local Capabilities or NetworkPolicy into core; the core API takes minimal placement DTOs.
• Kept existing error messages and zero-constraint semantics so downstream behavior can delegate without user-visible drift.
• No fallback implementation is introduced downstream; workflow-compute can reduce to an adapter shim.