test: 修复 Tailwind v4 测试夹具依赖解析

[sonofmagic]

变更

• 将真实执行的 Tailwind v4 测试夹具从已移除的 tailwindcss4 npm alias 切换到 tailwindcss
• 保留生产代码和专门测试中的历史 tailwindcss4 兼容契约
• 修复原生 v4 engine 回归用例的 Tailwind 入口解析

Related to #1053

验证

• pnpm build：61/61 tasks 通过
• 定向 Vitest：81/81 通过
• v4-engine.test.ts：61/61 通过
• 核心包完整测试（排除本机缺少浏览器二进制的 2 个 Playwright 用例）：3150/3150 通过
• git diff --check：通过

GitHub Actions 当前处于官方 major outage；待平台恢复后继续复跑并处理新 PR 的真实失败。

[changeset-bot]

⚠️ No Changeset found

Latest commit: be8dfda

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR