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

tests/server/checker/engine.test.ts

@@ -209,7 +209,7 @@ describe("ProbeEngine", () => {
       }),
     );
 
-    const mockStore = createMockStore(targets.map((t) => t.name)) as unknown as ProbeStore;
+    const mockStore = createMockStore(targets.map((t) => t.name ?? t.id)) as unknown as ProbeStore;
     const engine = new ProbeEngine(mockStore, targets, 2);
 
     const probeGroup = (