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/checker/store.test.ts

@@ -3,12 +3,12 @@ import { mkdir } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 
-import type { ResolvedCommandTarget } from "../../../src/server/checker/runner/command/types";
+import type { ResolvedCommandTarget } from "../../../src/server/checker/runner/cmd/types";
 import type { ResolvedHttpTarget } from "../../../src/server/checker/runner/http/types";
 import type { CheckFailure } from "../../../src/server/checker/types";
 
 import { checkerRegistry } from "../../../src/server/checker/runner";
-import { CommandChecker } from "../../../src/server/checker/runner/command/execute";
+import { CommandChecker } from "../../../src/server/checker/runner/cmd/execute";
 import { HttpChecker } from "../../../src/server/checker/runner/http/execute";
 import { ProbeStore } from "../../../src/server/checker/store";
 import { rmRetry } from "../../helpers";
@@ -42,7 +42,7 @@ const httpTarget: ResolvedHttpTarget = {
 };
 
 const commandTarget: ResolvedCommandTarget = {
-  command: {
+  cmd: {
     args: ["-c", "1", "localhost"],
     cwd: "/tmp",
     env: {},
@@ -53,7 +53,7 @@ const commandTarget: ResolvedCommandTarget = {
   intervalMs: 60000,
   name: "test-cmd",
   timeoutMs: 5000,
-  type: "command",
+  type: "cmd",
 };
 
 describe("ProbeStore", () => {
@@ -75,7 +75,7 @@ describe("ProbeStore", () => {
     expect(store.getTargets()).toHaveLength(0);
   });
 
-  test("同步 http 和 command targets", () => {
+  test("同步 http 和 cmd targets", () => {
     store.syncTargets([httpTarget, commandTarget]);
     const targets = store.getTargets();
     expect(targets).toHaveLength(2);
@@ -106,9 +106,9 @@ describe("ProbeStore", () => {
     expect(JSON.parse(t.expect!)).toEqual({ maxDurationMs: 3000, status: [200] });
   });
 
-  test("command target 字段正确", () => {
+  test("cmd target 字段正确", () => {
     const t = store.getTargets().find((t) => t.name === "test-cmd")!;
-    expect(t.type).toBe("command");
+    expect(t.type).toBe("cmd");
     expect(t.target).toBe("exec ping -c 1 localhost");
     const config = JSON.parse(t.config) as { args: string[]; cwd: string; exec: string; maxOutputBytes: number };
     expect(config.exec).toBe("ping");