refactor(schema): drop cli shim packages, add testseam swap, consolidate ForTest helpers

- import 统一：删除 cli/contractfinal 与 cli/runtimeannotate 垫片包，
  26 个消费文件一律直引 corecmd/*；cli 根仅保留 runtime_schema_seam.go
  包内别名，依赖图保持单向无环
- 新增 internal/testseam.Swap[T]：包级 var 注入缝置换由 t.Cleanup
  结构性恢复；迁移 pipeline*/stdinIsTerminalFn/loadReviewedCommandRegistry/
  schemaCommandCatalogError/schemaParameterBindingData/finalSchemaAgentMetadata
  六组核心缝（26+ 处）
- ForTest 辅助归拢到 per-package fortest.go（corecmd/contract、
  corecmd/contractfinal、shortcut、cli），生产文件只留真逻辑
- 文档同步：runtime_schema_seam.go / runtimeannotate/doc.go 注释、
  CHANGELOG、RFC §278-279、AGENTS.md

internal/generator/agentmetadata/contract_final_coverage_test.go

@@ -8,8 +8,8 @@ import (
 	"testing"
 
 	"github.com/DingTalk-Real-AI/dingtalk-workspace-cli/internal/cli"
-	"github.com/DingTalk-Real-AI/dingtalk-workspace-cli/internal/cli/contractfinal"
 	"github.com/DingTalk-Real-AI/dingtalk-workspace-cli/internal/corecmd/contract"
+	"github.com/DingTalk-Real-AI/dingtalk-workspace-cli/internal/corecmd/contractfinal"
 	"github.com/spf13/cobra"
 )