MM-63669 E2E/Playwright: Move "e2e-tests/playwright/test" to "e2e-tests/playwright" folder (#30647)

* move "e2e-tests/playwright/test" to  "e2e-tests/playwright/test" and expose "ensurePluginsLoaded"

* add test setup, and expose ensurePluginsLoaded and ensureServerDeployment to pw

e2e-tests/playwright/specs/functional/channels/message_priority/standard_priority.spec.ts

@@ -0,0 +1,48 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+import {expect, test} from '@mattermost/playwright-lib';
+
+test('MM-T5139: Message Priority - Standard message priority and system setting', async ({pw}) => {
+    // # Setup test environment
+    const {user} = await pw.initSetup();
+
+    // # Log in as a user in new browser context
+    const {channelsPage} = await pw.testBrowser.login(user);
+
+    // # Visit default channel page
+    await channelsPage.goto();
+    await channelsPage.toBeVisible();
+
+    // Open menu
+    await channelsPage.centerView.postCreate.openPriorityMenu();
+
+    // Use messagePriority for dialog interactions
+    await channelsPage.messagePriority.verifyPriorityDialog();
+    await channelsPage.messagePriority.verifyStandardOptionSelected();
+
+    // # Close menu and post message
+    await channelsPage.messagePriority.closePriorityMenu();
+
+    const testMessage = 'This is just a test message';
+    await channelsPage.postMessage(testMessage);
+
+    // # Verify message posts without priority label
+    const lastPost = await channelsPage.centerView.getLastPost();
+    await lastPost.toBeVisible();
+    await lastPost.toContainText(testMessage);
+    await expect(lastPost.container.locator('.post-priority')).not.toBeVisible();
+
+    // # Open post in RHS and verify
+    await lastPost.container.click();
+    await channelsPage.sidebarRight.toBeVisible();
+
+    // # Get RHS post and verify content
+    const rhsPost = await channelsPage.sidebarRight.getLastPost();
+    await rhsPost.toBeVisible();
+    await rhsPost.toContainText(testMessage);
+    await expect(rhsPost.container.locator('.post-priority')).not.toBeVisible();
+
+    // # Verify RHS formatting bar doesn't have priority button
+    await expect(channelsPage.sidebarRight.postCreate.priorityButton).not.toBeVisible();
+});