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。

src/server/checker/runner/cmd/schema.ts

@@ -0,0 +1,34 @@
+import { Type } from "@sinclair/typebox";
+
+import type { CheckerSchemas } from "../types";
+
+import { createTextRulesSchema, sizeSchema, stringMapSchema } from "../../schema/fragments";
+
+export const commandCheckerSchemas: CheckerSchemas = {
+  config: Type.Object(
+    {
+      args: Type.Optional(Type.Array(Type.String())),
+      cwd: Type.Optional(Type.String()),
+      env: Type.Optional(stringMapSchema),
+      exec: Type.String({ minLength: 1 }),
+      maxOutputBytes: Type.Optional(sizeSchema),
+    },
+    { additionalProperties: false },
+  ),
+  defaults: Type.Object(
+    {
+      cwd: Type.Optional(Type.String()),
+      maxOutputBytes: Type.Optional(sizeSchema),
+    },
+    { additionalProperties: false },
+  ),
+  expect: Type.Object(
+    {
+      exitCode: Type.Optional(Type.Array(Type.Integer())),
+      maxDurationMs: Type.Optional(Type.Number({ minimum: 0 })),
+      stderr: Type.Optional(createTextRulesSchema()),
+      stdout: Type.Optional(createTextRulesSchema()),
+    },
+    { additionalProperties: false },
+  ),
+};