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>

playwright.config.ts

@@ -5,6 +5,8 @@ const timeoutFactor = Number(env.GITEA_TEST_E2E_TIMEOUT_FACTOR) || 1;
 const timeout = 5000 * timeoutFactor;
 
 export default defineConfig({
+  workers: '50%',
+  fullyParallel: true,
   testDir: './tests/e2e/',
   outputDir: './tests/e2e-output/',
   testMatch: /.*\.test\.ts/,
@@ -28,11 +30,11 @@ export default defineConfig({
         permissions: ['clipboard-read', 'clipboard-write'],
       },
     },
-    ...env.CI ? [{
+    {
       name: 'firefox',
       use: {
         ...devices['Desktop Firefox'],
       },
-    }] : [],
+    },
   ],
 });