Add CI workflow

Author: slyhyun

.github/workflows/ci.yml

@@ -0,0 +1,40 @@
+name: CI
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up JDK 21
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: "21"
+          cache: gradle
+
+      - name: Make gradlew executable
+        run: chmod +x gradlew
+
+      - name: Run tests
+        run: ./gradlew test
+
+      - name: Upload test reports (always)
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: test-reports
+          path: |
+            **/build/reports/tests/test
+            **/build/test-results/test