refactor: 将 memory checker 重命名为 mem

- 类型标识符 memory → mem
- 类名 MemoryChecker → MemChecker
- 内部类型名统一 Memory* → Mem*
- 内部函数名统一 *Memory* → *Mem*
- 目录重命名 memory/ → mem/（源码、测试、文档）
- 配置键 memory: → mem:
- 重新生成 probe-config.schema.json
- 保留中文"内存"用户提示

破坏性变更：无向后兼容

tests/server/checker/runner/registry.test.ts

@@ -84,7 +84,7 @@ describe("CheckerRegistry", () => {
       "dns",
       "ws",
       "cpu",
-      "memory",
+      "mem",
       "custom",
     ]);
     expect(second.supportedTypes).toEqual([
@@ -98,7 +98,7 @@ describe("CheckerRegistry", () => {
       "dns",
       "ws",
       "cpu",
-      "memory",
+      "mem",
     ]);
     expect(
       first.definitions.every((checker) => checker.schemas.authoring.config && checker.schemas.normalized.expect),