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/README.md

@@ -0,0 +1,49 @@
+# kkFileView E2E MVP
+
+This folder contains a first MVP of end-to-end automated tests.
+
+## What is covered
+
+- Basic preview smoke checks for common file types (txt/md/json/xml/csv/html/png)
+- Basic endpoint reachability
+- Security regression checks for blocked internal-network hosts (`10.*`) on:
+  - `/onlinePreview`
+  - `/getCorsFile`
+
+## Local run
+
+1. Build server jar:
+
+```bash
+mvn -q -pl server -DskipTests package
+```
+
+2. Install deps + browser:
+
+```bash
+cd tests/e2e
+npm install
+npx playwright install --with-deps chromium
+```
+
+3. Generate fixtures and start fixture server:
+
+```bash
+cd /path/to/kkFileView
+node tests/e2e/scripts/generate-fixtures.mjs
+cd tests/e2e/fixtures && python3 -m http.server 18080
+```
+
+4. Start kkFileView in another terminal:
+
+```bash
+JAR_PATH=$(ls server/target/kkFileView-*.jar | head -n 1)
+KK_TRUST_HOST='*' KK_NOT_TRUST_HOST='10.*,172.16.*,192.168.*' java -jar "$JAR_PATH"
+```
+
+5. Run tests:
+
+```bash
+cd tests/e2e
+KK_BASE_URL=http://127.0.0.1:8012 FIXTURE_BASE_URL=http://127.0.0.1:18080 npm test
+```