ci(e2e): add Playwright-based E2E workflow for Mage-OS

.github/workflows/_internal-e2e.yaml

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+name: E2E Test
+
+on:
+  workflow_dispatch: {}
+  push:
+    branches:
+    - main
+    paths:
+    - "_test/demo-package/**"
+    - ".github/workflows/_internal-e2e.yaml"
+    - ".github/workflows/e2e.yaml"
+    - "supported-version/**"
+    - "!(**/*.md)"
+  pull_request:
+    branches:
+    - main
+    paths:
+    - "_test/demo-package/**"
+    - ".github/workflows/_internal-e2e.yaml"
+    - ".github/workflows/e2e.yaml"
+    - "supported-version/**"
+    - "!(**/*.md)"
+
+jobs:
+  check-demo-package:
+    runs-on: ubuntu-latest
+    outputs:
+      exists: ${{ steps.check.outputs.exists }}
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Check if folder exists
+        id: check
+        run: |
+          if [ -d "_test/demo-package" ]; then
+            echo "exists=true" >> $GITHUB_OUTPUT
+          else
+            echo "exists=false" >> $GITHUB_OUTPUT
+          fi
+
+  compute_matrix:
+      runs-on: ubuntu-latest
+      outputs:
+        matrix: ${{ steps.supported-version.outputs.matrix }}
+      steps:
+        - uses: actions/checkout@v4
+        - uses: ./supported-version
+          with:
+            kind: all
+          id: supported-version
+        - run: echo ${{ steps.supported-version.outputs.matrix }}
+  e2e-workflow:
+    if: needs.check-demo-package.outputs.exists == 'true'
+    needs: compute_matrix
+    uses: ./.github/workflows/e2e.yaml
+    with:
+      package_name: mage-os/magento2-demo-package
+      source_folder: $GITHUB_WORKSPACE/_test/demo-package
+      matrix: ${{ needs.compute_matrix.outputs.matrix }}
+      test_command: |
+        npx playwright test --grep "@setup" --trace on
+        npx playwright test --grep-invert "@setup" --trace on
+      fail-fast: false

.github/workflows/e2e-README.md

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+# End-to-End (E2E) Tests for Mage-OS / Magento
+
+A reusable GitHub Actions workflow that installs Magento (Mage-OS)
+and runs browser-based End-to-End (E2E) tests against a real storefront
+using Playwright or an equivalent E2E runner.
+
+## Inputs
+
+See the [e2e.yaml](./e2e.yaml)
+
+| Input              | Description                                                                                                                                     | Required | Default                       |
+| ------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------- | -------- | ----------------------------- |
+| matrix             | JSON string of [version matrix for Magento](./#matrix-format)                                                                                   | true     | NULL                          |
+| fail-fast          | Same as Github's [fail-fast](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idstrategyfail-fast) | false    | true                          |
+| package_name       | The name of the package                                                                                                                         | true     | NULL                          |
+| source_folder      | The source folder of the package                                                                                                                | false    | $GITHUB_WORKSPACE             |
+| magento_directory  | The folder where Magento will be installed                                                                                                      | false    | ../magento2                   |
+| magento_repository | Where to install Magento from                                                                                                                   | false    | https://mirror.mage-os.org/   |
+| test_command       | The e2e test command to run                                                                                                             | false    | "../../../vendor/bin/phpunit" |
+| composer_cache_key | A key to version the composer cache. Can be incremented if you need to bust the cache.                                                          | false    | ""                            |
+
+## Secrets
+| Input         | Description                                                                                                                             | Required | Default |
+| ------------- | --------------------------------------------------------------------------------------------------------------------------------------- | -------- | ------- |
+| composer_auth | JSON string of [composer credentials](https://devdocs.magento.com/guides/v2.4/install-gde/prereq/connect-auth.html) | false    | NULL    |
+> The `test_command` is executed from the Magento installation directory.
+> E2E tests are expected to live under `dev/tests/e2e`.
+
+###  Matrix Format
+
+The Magento matrix format outlined by the [supported versions action.](https://github.com/mage-os/github-actions/tree/main/supported-version/supported.json) 
+
+
+## E2E execution model
+
+The E2E test suite is executed in two phases:
+
+### 1. Setup phase
+
+The setup phase prepares shared browser state (e.g. authenticated sessions,
+cookies, required entities). This phase is marked using the `@setup` tag.
+
+```bash
+npx playwright test --grep "@setup" --trace on
+```
+
+This step is required once per fresh environment.
+
+### 2. Test phase
+
+Once setup has completed successfully, the full E2E test suite can be executed.
+Setup tests are skipped using --grep-invert.
+
+```bash
+npx playwright test --grep-invert "@setup" --trace on
+```
+
+This phase validates real user journeys against a live Magento storefront.
+
+```yml
+name: E2E Test
+
+on:
+  push:
+    branches:
+    - main
+  pull_request:
+    branches:
+    - main
+
+jobs:
+  compute_matrix:
+      runs-on: ubuntu-latest
+      outputs:
+        matrix: ${{ steps.supported-version.outputs.matrix }}
+      steps:
+        - uses: actions/checkout@v2
+        - uses: mage-os/github-actions/supported-version@main
+          id: supported-version
+        - run: echo ${{ steps.supported-version.outputs.matrix }}
+  e2e-workflow:
+    needs: compute_matrix
+    uses: mage-os/github-actions/.github/workflows/e2e.yaml@main
+    with:
+      package_name: my-vendor/package
+      matrix: ${{ needs.compute_matrix.outputs.matrix }}
+      test_command: |
+          npx playwright test --grep "@setup" --trace on
+          npx playwright test --grep-invert "@setup" --trace on
+  secrets:
+      composer_auth: ${{ secrets.COMPOSER_AUTH }}
+```