test: add automated PHP, JS, and E2E suites with CI

[firestar300]

Add wp-env test setup, PHPUnit integration tests, Jest unit tests for tabs behavior, Playwright editor and frontend specs, and GitHub workflows. Extract TabsAutomatic for testability, drop Psalm, and stop versioning composer.lock.

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Note

Medium Risk
Editor attribute sync and react-jsx-runtime polyfill affect block registration on older WordPress; KSES change affects saved tab markup. Most risk is in small production PHP/JS fixes alongside large test-only additions.

Overview
Adds automated testing end-to-end: PHPUnit integration tests in an isolated wp-env instance (.wp-env.test.json, port 8889), Jest unit tests for TabsAutomatic and icon-block helpers, and Playwright specs for block insertion in the editor and frontend ARIA/keyboard behavior. Three GitHub Actions workflows run PHP (matrix PHP 8.1/8.3 and WP 6.2 vs latest), JS unit tests, and E2E (with build/Chromium artifact caching).

Tooling changes: Psalm and psalm.xml.dist are removed; PHPUnit and wp-phpunit are added; composer.lock is gitignored; README documents local test commands; ESLint overrides for Jest/Playwright test files.

Runtime/editor fixes bundled with testability work: Frontend TabsAutomatic is extracted to tabs-automatic.js and imported from script.js. useSynchedID and tabsIndex updates move into useEffect/useSelect so attributes are not set during render. Inner blocks use directInsert: false (replacing experimental API). PHP allows aria-controls in KSES and registers a react-jsx-runtime webpack polyfill plus register_react_jsx_runtime() so editor scripts load on WordPress before 6.6.

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