Adds github actions.

.github/workflows/gradle.yml

@@ -0,0 +1,45 @@
+name: Java CI with Gradle
+
+on:
+  push:
+    branches: [ "develop" ]
+  pull_request:
+    branches: [ "develop" ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+
+    steps:
+      - uses: actions/checkout@v7
+
+      - name: Set up JDK 25
+        uses: actions/setup-java@v6
+        with:
+          java-version: '25'
+          distribution: 'temurin'
+
+      - name: Setup Gradle 9.8.0
+        uses: gradle/actions/setup-gradle@v5
+        with:
+          gradle-version: '9.8.0'
+          cache-read-only: ${{ github.ref != 'refs/heads/develop' }}
+
+      - name: Build with Gradle Wrapper
+        run: ./tools/build-plugin.sh
+
+      - name: Extract Project Version
+        id: project_info
+        run: |
+          VERSION=$(./gradlew properties --no-daemon -q | awk -F ': ' '$1 == "version" {print $2}')
+          echo "version=$VERSION" >> $GITHUB_OUTPUT
+
+      - name: Upload Plugin Artifact
+        uses: actions/upload-artifact@v7
+        with:
+          name: Metropolis-${{ steps.project_info.outputs.version }}
+          path: build/libs/*.jar
+          if-no-files-found: error
+          retention-days: 14