refactor(schema): drop dead cli.RegisterRuntimeContractFinal wrapper and legacy catalog label

- 删除 cli.RegisterRuntimeContractFinal 包装器：生产侧零调用（全部走
  corecmd.New 内部注册或 contractfinal 直调），9 处测试调用迁移到
  contractfinal.RegisterRuntimeContractFinal
- 删除死常量 ProvenanceEmbeddedCommandCatalog（全库零引用的 legacy
  wire label；运行时装配统一打 SchemaSourceRuntimeAssembled）
- 同步 6 处文档/注释：AGENTS.md、RFC §277、contract/final.go、
  contractfinal/store.go、contractfinal/doc.go、corecmd.go、
  contract/doc.go、contract_register_seam_test.go 的死符号钉扎改为
  import 前缀分层检查兜底

internal/generator/agentmetadata/contract_final_coverage_test.go

@@ -44,7 +44,7 @@ func TestCrossPlatformCoverageContractFinalSkipsWithoutOverlay(t *testing.T) {
 
 func TestCrossPlatformCoverageContractFinalMissingCanonicalProjection(t *testing.T) {
 	declared := &cobra.Command{Use: "run"}
-	cli.RegisterRuntimeContractFinal(declared, contract.ContractFinalPayload{
+	contractfinal.RegisterRuntimeContractFinal(declared, contract.ContractFinalPayload{
 		Selection: &contract.SelectionSpec{
 			AgentSummary: "Declared",
 			UseWhen:      []string{"use"},
@@ -142,7 +142,7 @@ func TestCrossPlatformCoverageContractFinalProductDeclMergeConflicts(t *testing.
 
 func TestCrossPlatformCoverageContractFinalToolMergeConflict(t *testing.T) {
 	declared := &cobra.Command{Use: "run"}
-	cli.RegisterRuntimeContractFinal(declared, contract.ContractFinalPayload{
+	contractfinal.RegisterRuntimeContractFinal(declared, contract.ContractFinalPayload{
 		Selection: &contract.SelectionSpec{
 			AgentSummary: "Declared summary",
 			UseWhen:      []string{"use declared"},