feat: 新增 ICMP/Ping checker，支持跨平台主机存活检测与延迟监控

实现 type: ping checker，通过 Bun.spawn 调用系统 ping 命令，自行实现跨平台
输出解析器（Linux/macOS/Windows 含中文 locale），支持 alive、丢包率、延迟、
耗时等 expect 断言，复用现有 checker 架构零外部依赖。

包含完整的类型定义、TypeBox schema、语义校验、命令构建、解析、断言、执行、
注册、配置加载测试，以及 probe-config.schema.json 更新和文档更新。

审查修复：提取 buildPingCommand 为独立纯函数并补充跨平台单测，补充
maxDurationMs/maxAvgLatencyMs 类型非法和空字符串 host 边界测试用例。

变更已归档，delta specs 已同步至 main specs。

probe-config.schema.json

@@ -83,6 +83,11 @@
               ]
             }
           }
+        },
+        "ping": {
+          "additionalProperties": false,
+          "type": "object",
+          "properties": {}
         }
       }
     },
@@ -1142,6 +1147,107 @@
                 }
               }
             }
+          },
+          {
+            "additionalProperties": false,
+            "type": "object",
+            "required": [
+              "id",
+              "type",
+              "ping"
+            ],
+            "properties": {
+              "description": {
+                "anyOf": [
+                  {
+                    "type": "null"
+                  },
+                  {
+                    "maxLength": 500,
+                    "type": "string"
+                  }
+                ]
+              },
+              "expect": {
+                "additionalProperties": false,
+                "type": "object",
+                "properties": {
+                  "alive": {
+                    "type": "boolean"
+                  },
+                  "maxAvgLatencyMs": {
+                    "minimum": 0,
+                    "type": "number"
+                  },
+                  "maxDurationMs": {
+                    "minimum": 0,
+                    "type": "number"
+                  },
+                  "maxMaxLatencyMs": {
+                    "minimum": 0,
+                    "type": "number"
+                  },
+                  "maxPacketLoss": {
+                    "maximum": 100,
+                    "minimum": 0,
+                    "type": "number"
+                  }
+                }
+              },
+              "group": {
+                "type": "string"
+              },
+              "id": {
+                "maxLength": 30,
+                "minLength": 1,
+                "type": "string"
+              },
+              "interval": {
+                "type": "string"
+              },
+              "name": {
+                "anyOf": [
+                  {
+                    "type": "null"
+                  },
+                  {
+                    "maxLength": 30,
+                    "minLength": 1,
+                    "type": "string"
+                  }
+                ]
+              },
+              "timeout": {
+                "type": "string"
+              },
+              "type": {
+                "const": "ping",
+                "type": "string"
+              },
+              "ping": {
+                "additionalProperties": false,
+                "type": "object",
+                "required": [
+                  "host"
+                ],
+                "properties": {
+                  "count": {
+                    "maximum": 100,
+                    "minimum": 1,
+                    "type": "integer"
+                  },
+                  "host": {
+                    "minLength": 1,
+                    "type": "string"
+                  },
+                  "packetSize": {
+                    "maximum": 65500,
+                    "minimum": 1,
+                    "type": "integer"
+                  }
+                }
+              }
+            }
           }
         ]
       }