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/package.json

@@ -0,0 +1,14 @@
+{
+  "name": "kkfileview-e2e",
+  "private": true,
+  "version": "0.1.0",
+  "type": "module",
+  "scripts": {
+    "test": "playwright test",
+    "test:headed": "playwright test --headed",
+    "gen:fixtures": "node ./scripts/generate-fixtures.mjs"
+  },
+  "devDependencies": {
+    "@playwright/test": "^1.55.0"
+  }
+}