refactor: 统一 target name/description 可空语义，前端展示 fallback 到 id

- schema: name/description 允许省略或显式 null，TypeBox Union([Null, String])
- 类型: RawTargetConfig/ResolvedTargetBase/子类型/StoredTarget/TargetStatus name 改为 string | null
- checker resolve: name: t.name ?? null，不再 fallback 到 id
- 语义校验: 拒绝空字符串和纯空白 name
- SQLite: targets.name 列改为可空 TEXT
- 前端: 新增 getTargetDisplayName(target) 展示 name ?? id
- 测试: 覆盖 name/description null 全场景，查找改为按 id
- 文档: 更新 README/DEVELOPMENT 和 6 个 openspec specs

src/server/checker/config-loader.ts

@@ -179,6 +179,10 @@ function validateConfig(config: RawProbeConfig): ConfigValidationIssue[] {
     const nameValue: unknown = raw["name"];
     const name = isString(nameValue) ? nameValue : id;
 
+    if (isString(nameValue) && nameValue.trim() === "") {
+      issues.push(issue("invalid-value", `targets[${i}].name`, "name 不能为空白", name));
+    }
+
     const type: unknown = raw["type"];
     if (!isString(type)) {
       issues.push(issue("required", `targets[${i}].type`, "缺少 type 字段", name));