Add pr-review e2e test and speed up e2e tests (#37345)

- add pr-review e2e test
- speed up most tests by logging in via POST to avoid the login form,
login form is still exercised in a dedicated test
- speed up most tests be removing post-test cleanup, unnecessary because
each repo is created with a unique name
- misc parallelization and api call reduction
- total suite runtime is about the same as before

---------

Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

tests/e2e/register.test.ts

@@ -1,6 +1,6 @@
 import {env} from 'node:process';
 import {test, expect} from '@playwright/test';
-import {login, logout, apiDeleteUser, randomString} from './utils.ts';
+import {login, logout, randomString} from './utils.ts';
 
 test.beforeEach(async ({page}) => {
   await page.goto('/user/sign_up');
@@ -48,9 +48,6 @@ test('register then login', async ({page}) => {
   // Logout then login with the newly created account
   await logout(page);
   await login(page, username, password);
-
-  // delete via API because of issues related to form-fetch-action
-  await apiDeleteUser(page.request, username);
 });
 
 test('register with existing username shows error', async ({page}) => {