test: 添加完整测试套件（52 个文件，326 个用例）

基于 Vitest 搭建测试基础设施，覆盖后端纯函数、API 路由、
前端 hooks、UI 组件和页面级集成测试。

vitest.config.ts

@@ -0,0 +1,25 @@
+import { defineConfig } from "vitest/config";
+import react from "@vitejs/plugin-react";
+import path from "path";
+
+export default defineConfig({
+  plugins: [react()],
+  resolve: {
+    alias: {
+      "@": path.resolve(__dirname, "src"),
+    },
+  },
+  test: {
+    globals: true,
+    environment: "jsdom",
+    setupFiles: ["src/__tests__/helpers/setup.ts"],
+    environmentMatchGlobs: [
+      ["src/app/api/**/*.test.ts", "node"],
+      ["src/lib/**/*.test.ts", "node"],
+    ],
+    env: {
+      AMAP_API_KEY: "test-amap-key",
+      DEEPSEEK_API_KEY: "test-deepseek-key",
+    },
+  },
+});