Build: add a PW testing style guide

[dominikvagner]

Summary

This adds a style guide for writing Playwright tests. 💅🏼

[sourcery-ai]

Reviewer's Guide

This PR adds a comprehensive Markdown-based Playwright testing style guide under _playwright-tests/style_guide.md, standardizing best practices, test structure, selectors, assertions, debugging workflows, and known caveats.

File-Level Changes

Change	Details	Files
Add Playwright style guide documentation	Create new style_guide.md file in _playwright-tests Populate with purpose, TOC, and introduction tip	_playwright-tests/style_guide.md
Define best practices for Playwright tests	Enumerate guidelines on isolation, idempotency, parallelization, and built-in capture features Advise minimal abstractions, selective helpers/fixtures, and clear test descriptions	_playwright-tests/style_guide.md
Establish recommended test structure	Describe folder/file hierarchy for utils, UI, and integration tests Provide example TypeScript spec with beforeEach, test.step, and imports	_playwright-tests/style_guide.md
Outline selector strategy preferences	Rank selectors: roles, text, test IDs, CSS, and discourage XPath and style-dependent locators Include code examples for each primary strategy	_playwright-tests/style_guide.md
Document assertion patterns	Recommend Playwright web-first assertions (toBeVisible, toHaveText, etc.) Show polling and promise patterns for non-DOM checks	_playwright-tests/style_guide.md
Detail debugging techniques	Cover Playwright Inspector (--debug), trace viewer config, and page.pause() Mention VS Code extension for live debugging	_playwright-tests/style_guide.md
Highlight caveats and workarounds	Warn about modal/dialog interaction issues and provide locator workaround Note flaky navigation scenarios and suggest retry logic	_playwright-tests/style_guide.md

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[sourcery-ai]

Hey @dominikvagner - I've reviewed your changes and they look great!

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[sourcery-ai]

Hey @dominikvagner - I've reviewed your changes and they look great!

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[marusak]

Can you please add one more good practice - don't use sleep. If you need to wait for something, define it same way as user would wait for it. Sleeps make tests flaky and/or slow.

[marusak]

Thanks!