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/app.test.ts

@@ -12,7 +12,7 @@ import type {
 } from "../../src/shared/api";
 
 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 { startServer } from "../../src/server/server";
@@ -56,7 +56,7 @@ describe("API 路由", () => {
         type: "http",
       },
       {
-        command: {
+        cmd: {
           args: ["hello"],
           cwd: "/tmp",
           env: {},
@@ -67,7 +67,7 @@ describe("API 路由", () => {
         intervalMs: 60000,
         name: "test-b",
         timeoutMs: 5000,
-        type: "command",
+        type: "cmd",
       },
     ]);
 
@@ -150,7 +150,7 @@ describe("API 路由", () => {
     expect(tA.stats.availability).toBeDefined();
 
     const tB = body.find((t) => t.name === "test-b")!;
-    expect(tB.type).toBe("command");
+    expect(tB.type).toBe("cmd");
     expect(tB.target).toBe("exec echo hello");
     expect(tB.latestCheck).toBeNull();
   });
@@ -162,7 +162,7 @@ describe("API 路由", () => {
     expect(response.status).toBe(200);
     expect(body.checkerTypes).toEqual(checkerRegistry.supportedTypes);
     expect(body.checkerTypes).toContain("http");
-    expect(body.checkerTypes).toContain("command");
+    expect(body.checkerTypes).toContain("cmd");
   });
 
   test("不支持的 method 在有 API 通配符时返回 404", async () => {