fix(engine): stabilize schema target extraction order

[Patel230]

Summary

• make schema-based target extraction deterministic instead of relying on Go map iteration order
• prioritize source-like keys before destination-like keys for multi-path tool schemas
• remove the flake behind the current main CI failure in internal/engine

Verification

• GOCACHE=/private/tmp/hawk-main-gocache go test ./internal/engine -race -count=20 -shuffle=on -run TestExtractTargetsFromSchema
• GOCACHE=/private/tmp/hawk-main-gocache go test ./internal/engine -race -count=1 -shuffle=on