refactor: 重命名 command checker 为 cmd checker 并适配跨平台测试

将 type/configKey 从 "command" 统一为 "cmd"，源码目录 runner/command/ → runner/cmd/，
spec 目录 command-checker/ → cmd-checker/，测试全部改用 bun -e 替代 Unix 系统命令，
归档 cmd-checker-enhancement 变更并同步 delta spec 到主 spec。

tests/server/bootstrap.test.ts

@@ -15,7 +15,7 @@ const target: ResolvedTargetBase = {
   intervalMs: 30000,
   name: "test",
   timeoutMs: 5000,
-  type: "command",
+  type: "cmd",
 };
 
 function createHarness(overrides: BootstrapDependencies = {}) {