Simplify stage and Audita contracts

internal/stage/stage.go

@@ -40,16 +40,9 @@ type Env struct {
 	RevalidatePublishLocks func(context.Context) ([]config.PublishLockRule, error)
 }
 
-// IODecl declares the intended input/output artifact kinds for a stage.
-type IODecl struct {
-	Inputs  []artifacts.Ref
-	Outputs []artifacts.Ref
-}
-
 // Stage is the pipeline unit contract.
 type Stage interface {
 	Name() string
-	Declares() IODecl
 	Run(ctx context.Context, env *Env, m *manifest.Manifest) (*StageResult, error)
 }