fix: 修复 Antigravity 账号 intercept_warmup_requests 配置无法保存

提取 applyInterceptWarmup 纯函数统一所有调用点：
- 修复 upstream 创建时遗漏写入 intercept_warmup_requests
- 修复 apikey 编辑时缺少 else 清除逻辑
- 添加前后端单元测试
- 修复 vitest.config.ts mergeConfig 兼容性问题

frontend/vitest.config.ts

@@ -1,35 +1,37 @@
-import { defineConfig, mergeConfig } from 'vitest/config'
-import viteConfig from './vite.config'
+import { defineConfig } from 'vitest/config'
+import { resolve } from 'path'
 
-export default mergeConfig(
-  viteConfig,
-  defineConfig({
-    test: {
-      globals: true,
-      environment: 'jsdom',
-      include: ['src/**/*.{test,spec}.{js,ts,jsx,tsx}'],
-      exclude: ['node_modules', 'dist'],
-      coverage: {
-        provider: 'v8',
-        reporter: ['text', 'json', 'html'],
-        include: ['src/**/*.{js,ts,vue}'],
-        exclude: [
-          'node_modules',
-          'src/**/*.d.ts',
-          'src/**/*.spec.ts',
-          'src/**/*.test.ts',
-          'src/main.ts'
-        ],
-        thresholds: {
-          global: {
-            statements: 80,
-            branches: 80,
-            functions: 80,
-            lines: 80
-          }
-        }
-      },
-      setupFiles: ['./src/__tests__/setup.ts']
+export default defineConfig({
+  resolve: {
+    alias: {
+      '@': resolve(__dirname, 'src'),
+      'vue-i18n': 'vue-i18n/dist/vue-i18n.runtime.esm-bundler.js'
     }
-  })
-)
+  },
+  test: {
+    globals: true,
+    environment: 'jsdom',
+    include: ['src/**/*.{test,spec}.{js,ts,jsx,tsx}'],
+    exclude: ['node_modules', 'dist'],
+    coverage: {
+      provider: 'v8',
+      reporter: ['text', 'json', 'html'],
+      include: ['src/**/*.{js,ts,vue}'],
+      exclude: [
+        'node_modules',
+        'src/**/*.d.ts',
+        'src/**/*.spec.ts',
+        'src/**/*.test.ts',
+        'src/main.ts'
+      ],
+      thresholds: {
+        global: {
+          statements: 80,
+          branches: 80,
+          functions: 80,
+          lines: 80
+        }
+      }
+    }
+  }
+})