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。

probe-config.schema.json

@@ -70,7 +70,7 @@
             }
           }
         },
-        "command": {
+        "cmd": {
           "additionalProperties": false,
           "type": "object",
           "properties": {
@@ -524,7 +524,7 @@
             "required": [
               "name",
               "type",
-              "command"
+              "cmd"
             ],
             "properties": {
               "expect": {
@@ -673,10 +673,10 @@
                 "type": "string"
               },
               "type": {
-                "const": "command",
+                "const": "cmd",
                 "type": "string"
               },
-              "command": {
+              "cmd": {
                 "additionalProperties": false,
                 "type": "object",
                 "required": [