Add e2e reaction test, improve accessibility, enable parallel testing (#37081)

Add a new e2e test for toggling issue reactions via the reaction picker
dropdown.

Add `aria-label` attributes to improve reaction accessibility:
- Add `aria-label="Reaction"` to the reaction picker dropdown
- Add `role="group"` with `aria-label="Reactions"` to the reactions
container, giving it a semantic identity for screen readers
- Include the reaction key in each reaction button's `aria-label` (e.g.
`+1: user1, user2`) so screen readers announce which reaction a button
represents

E2e test improvements:
- Simplify `randomString` to use `Math.random` instead of `node:crypto`
- Replace `generatePassword` with a static password, remove unused
`clickDropdownItem`
- Enable `fullyParallel: true` and `workers: '50%'` in Playwright config
- Run both chromium and firefox in all environments (not just CI)
- Parallelize `login` and `apiCreateRepo` setup where possible
- Use dedicated test user in `user-settings` test for concurrency safety

Co-authored-by: Claude (Opus 4.6) <noreply@anthropic.com>

tests/e2e/codeeditor.test.ts

@@ -1,12 +1,11 @@
 import {env} from 'node:process';
 import {expect, test} from '@playwright/test';
-import {login, apiCreateRepo, apiDeleteRepo} from './utils.ts';
+import {login, apiCreateRepo, apiDeleteRepo, randomString} from './utils.ts';
 
 test('codeeditor textarea updates correctly', async ({page, request}) => {
-  const repoName = `e2e-codeeditor-${Date.now()}`;
-  await apiCreateRepo(request, {name: repoName});
+  const repoName = `e2e-codeeditor-${randomString(8)}`;
+  await Promise.all([apiCreateRepo(request, {name: repoName}), login(page)]);
   try {
-    await login(page);
     await page.goto(`/${env.GITEA_TEST_E2E_USER}/${repoName}/_new/main`);
     await page.getByPlaceholder('Name your file…').fill('test.js');
     await expect(page.locator('.editor-loading')).toBeHidden();