Add GitHub Actions CI workflow

Author: anyulled

.github/workflows/ci.yml

@@ -0,0 +1,30 @@
+name: Java CI with Maven
+
+on:
+  push:
+    branches: [ "main", "solution" ]
+  pull_request:
+    branches: [ "main", "solution" ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up JDK 25
+      uses: actions/setup-java@v4
+      with:
+        java-version: '25'
+        distribution: 'temurin'
+        cache: maven
+
+    - name: Build with Maven
+      run: ./mvnw clean verify -Popenai -B
+
+    - name: Upload Build Artifact
+      uses: actions/upload-artifact@v4
+      with:
+        name: battle-contender-jar
+        path: target/*.jar