Migrate E2E tests from @wordpress/env to WordPress Playground

[mattheu]

Summary

• Replaces Docker-based @wordpress/env with WordPress Playground (@wp-playground/cli), fixing the CI hangs and apt-lock issues from previous PRs
• Playground boots and tears down automatically within the test run — no separate start/stop steps in CI
• Adds a PHP × WP version matrix (PHP 8.3/8.4 × WP 6.8/6.9/latest) for better compatibility coverage

Changes

File	Change
blueprint.json	New — defines Playground env: WP 6.9, PHP 8.3, TwentyTwentyFive, Advanced Query Loop, mu-plugins, 25 seeded test posts
global-setup.js	New (project root) — boots Playground, saves auth state
global-teardown.js	New (project root) — shuts down Playground after tests
playwright.config.js	Dynamic WP_BASE_URL, 120s timeout, points to new setup/teardown
.github/workflows/playwright-tests.yml	Removes Docker/wp-env steps, adds PHP/WP matrix
tests/e2e/fixtures.js	Removes wpCli/resetDatabase (wp-env specific)
tests/e2e/global-setup.js	Deleted — replaced by project-root version
package.json	Adds @wp-playground/cli, removes @wordpress/env, updates scripts
CLAUDE.md	Updates testing docs to reflect Playground setup

Test plan

• Run npm run build && npm run test:e2e locally to verify Playground boots and all tests pass
• Confirm CI passes across the full PHP/WP matrix on this PR

🤖 Generated with Claude Code

[github-actions]

Playwright test results

 10 failed
 8 passed

Details

 18 tests across 6 suites
 12 minutes, 27 seconds
 f354f50

Failed tests

chromium › elasticpress-toggle.spec.js › ElasticPress Toggle › should show the Use ElasticSearch toggle in the panel
chromium › elasticpress-toggle.spec.js › ElasticPress Toggle › should toggle the Use ElasticSearch setting on and off
chromium › exclude-with-post-in.spec.js › Exclude Displayed Posts with post__in › should exclude displayed posts even when post__in is set via Advanced Query Loop
chromium › exclude-with-post-in.spec.js › Exclude Displayed Posts with post__in › should properly filter post__in array when multiple post templates used
chromium › posts-per-page.spec.js › Posts Per Page Override › should show posts per page control when query inherits
chromium › posts-per-page.spec.js › Posts Per Page Override › should reflect posts per page override in editor
chromium › posts-per-page.spec.js › Posts Per Page Override › should enforce max value from posts_per_page setting
chromium › query-presets.spec.js › Query Presets › should show query preset dropdown when presets are registered
chromium › query-presets.spec.js › Query Presets › should change post order when selecting alphabetical preset in editor
chromium › query-presets.spec.js › Query Presets › should change post order when selecting Z-A preset in editor