feat: add form validation test scenarios

[Rohini2222]

Summary

Adds end-to-end form validation tests using Playwright's TodoMVC demo app.

Test scenarios covered

• Empty input does not add a todo item
• Whitespace-only input is rejected
• Valid input successfully adds a todo item
• Input field clears after valid submission
• Multiple valid items can be added sequentially

How to run

npx playwright test tests/form-validation.spec.ts

[Rohini2222]

@microsoft-github-policy-service agree