ci: 更新 Playwright 配置以使用预览服务器

- 将 baseURL 固定为 http://localhost:4173，不再根据环境变量区分 CI 和本地环境
- 修改启动命令为先构建再启动预览服务器
- 设置 reuseExistingServer 为 true，优化服务器重用逻辑

(cherry picked from commit df6ffb99c8)

playwright.config.ts

@@ -2,7 +2,7 @@ import { defineConfig, devices } from '@playwright/test'
 import process from 'node:process'
 
 // const runningInVSCode = process.env.TERM_PROGRAM === 'vscode'
-const baseURL = process.env.CI ? 'http://localhost:4173' : 'http://localhost:4730'
+const baseURL = 'http://localhost:4173'
 
 /**
  * Read environment variables from file.
@@ -106,8 +106,8 @@ export default defineConfig({
      * Use the preview server on CI for more realistic testing.
      * Playwright will re-use the local server if there is already a dev-server running.
      */
-    command: process.env.CI ? 'pnpm run preview' : 'pnpm run dev',
+    command: 'pnpm run build-only; pnpm run preview',
     port: Number(new URL(baseURL).port),
-    reuseExistingServer: !process.env.CI,
+    reuseExistingServer: true /* !process.env.CI */,
   },
 })