Playwright e2e test for taborder

This should be a failing test for Firefox (but working in Chrome?) for
the taborder in the explore page.

Tabbing through the page should ensure that certain elements are focused
at least once.

tests/e2e/explore.test.e2e.js

@@ -0,0 +1,39 @@
+// @ts-check
+// document is a global in evaluate, so it's safe to ignore here
+/* eslint no-undef: 0 */
+import {test, expect} from '@playwright/test';
+
+test('Explore view taborder', async ({page}) => {
+  await page.goto('/explore/repos');
+
+  const l1 = page.locator('[href="https://forgejo.org"]');
+  const l2 = page.locator('[href="/assets/licenses.txt"]');
+  const l3 = page.locator('[href*="/stars"]').first();
+  const l4 = page.locator('[href*="/forks"]').first();
+  let res = 0;
+  const exp = 15; // 0b1111 = four passing tests
+
+  for (let i = 0; i < 150; i++) {
+    await page.keyboard.press('Tab');
+    if (await l1.evaluate((node) => document.activeElement === node)) {
+      res |= 1;
+      continue;
+    }
+    if (await l2.evaluate((node) => document.activeElement === node)) {
+      res |= 1 << 1;
+      continue;
+    }
+    if (await l3.evaluate((node) => document.activeElement === node)) {
+      res |= 1 << 2;
+      continue;
+    }
+    if (await l4.evaluate((node) => document.activeElement === node)) {
+      res |= 1 << 3;
+      continue;
+    }
+    if (res === exp) {
+      break;
+    }
+  }
+  await expect(res).toBe(exp);
+});