test(e2e): add MVP end-to-end automation suite and CI workflow (#713)

* test(e2e): add mvp playwright suite and PR workflow

* ci(e2e): use JDK 21 for kkFileView build

tests/e2e/playwright.config.ts

@@ -0,0 +1,11 @@
+import { defineConfig } from '@playwright/test';
+
+export default defineConfig({
+  testDir: './specs',
+  timeout: 30_000,
+  expect: { timeout: 10_000 },
+  reporter: [['list'], ['html', { outputFolder: 'playwright-report', open: 'never' }]],
+  use: {
+    baseURL: process.env.KK_BASE_URL || 'http://127.0.0.1:8012',
+  },
+});