ci: integrated visual tests via playwright

[makhnatkin]

This PR introduces Playwright visual testing to ensure UI consistency in PRs, enhancing code quality and preventing unintended UI changes.

What's Included?

1. GitHub Workflows

• PR Visual Tests – Runs Playwright visual tests for every PR.
• PR Visual Tests Report – Posts test reports as comments in the PR.

2. New Commands in package.json

To streamline testing, the following commands have been added:

• playwright:install – Installs Playwright with Chromium and Webkit
• playwright – Runs visual tests
• playwright:update – Updates snapshots
• playwright:clear – Clears test cache
• playwright:report – Displays test results report
• playwright:docker – Runs tests in Docker for local pre-PR validation
• playwright:docker:update – Updates snapshots in Docker for consistency across environments
• playwright:docker:clear – Clears cache in Docker for local testing
• playwright:docker:report – Displays test results report in Docker

3. Dependencies Added

• @playwright/test – Core package for running Playwright tests.
• @playwright/experimental-ct-react – Enables React component testing via Playwright. (Experimental Storybook package)

4. Test Configuration

• playwright.config.ts – Configures tests to run in Chromium and Webkit with React support via Vite.
• Defines test directory, generates HTML reports

5. Visual Tests

Snapshots are stored in __snapshots__ for verification.

6. Documentation

Added a new doc explaining Playwright visual testing, setup, and usage.

[gravity-ui-bot]

Preview is ready.