test: add tests for static asset serving and path traversal

[chenjiahan]

Summary

Add test cases to verify static file serving functionality and security against path traversal attacks.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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Lighthouse	1 paths audited Performance: 46 (🔴 down 15 from production) Accessibility: 97 (no change from production) Best Practices: 100 (no change from production) SEO: 100 (no change from production) PWA: 60 (no change from production) View the detailed breakdown and full score reports

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[Copilot]

Pull Request Overview

Adds comprehensive end-to-end tests for static asset serving functionality and security validation against path traversal attacks in the Rsbuild server.

• Creates test cases to verify static file serving from both public directory and built assets
• Implements security tests to ensure path traversal attacks return 403 Forbidden responses
• Sets up test infrastructure with sample assets and JavaScript files

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
e2e/cases/server/serve-assets/src/index.js	Adds sample JavaScript file for testing static asset serving
e2e/cases/server/serve-assets/public/foo.txt	Creates test asset file in public directory
e2e/cases/server/serve-assets/index.test.ts	Implements test cases for static serving and path traversal security

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