Add GitHub Actions workflow for Minecraft mod build

This workflow builds a Minecraft mod on push and creates a GitHub release with the mod artifact.

.github/workflows/build.yml

@@ -0,0 +1,105 @@
+name: Build Minecraft Mod
+
+on:
+  push:
+    branches: [ main ]
+  release:
+    types: [ published ]
+
+jobs:
+  build:
+    name: Build Mod
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up JDK 17
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: 17
+
+      - name: Grant execute permission for Gradle
+        run: chmod +x gradlew
+
+      - name: Build mod
+        run: ./gradlew build
+
+      - name: Read mod name and version
+        id: mod_info
+        run: |
+          NAME=$(grep "^archives_base_name" gradle.properties | cut -d'=' -f2)
+          VERSION=$(grep "^mod_version" gradle.properties | cut -d'=' -f2)
+
+          if [ -z "$NAME" ] || [ -z "$VERSION" ]; then
+            echo "Failed to read mod info from gradle.properties"
+            exit 1
+          fi
+
+          JAR="build/libs/${NAME}-${VERSION}.jar"
+
+          if [ ! -f "$JAR" ]; then
+            echo "Expected jar not found: $JAR"
+            exit 1
+          fi
+
+          echo "name=$NAME" >> $GITHUB_OUTPUT
+          echo "version=$VERSION" >> $GITHUB_OUTPUT
+          echo "jar=$JAR" >> $GITHUB_OUTPUT
+
+      - name: Upload mod artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: minecraft-mod
+          path: ${{ steps.mod_info.outputs.jar }}
+
+  create-release:
+    name: Create GitHub Release
+    runs-on: ubuntu-latest
+    needs: build
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Download mod artifact
+        uses: actions/download-artifact@v4
+        with:
+          name: minecraft-mod
+          path: ./release-artifacts/
+
+      - name: Read mod info again (for tagging)
+        id: mod_info
+        run: |
+          NAME=$(grep "^archives_base_name" gradle.properties | cut -d'=' -f2)
+          VERSION=$(grep "^mod_version" gradle.properties | cut -d'=' -f2)
+          echo "name=$NAME" >> $GITHUB_OUTPUT
+          echo "version=$VERSION" >> $GITHUB_OUTPUT
+
+      - name: Find next available release tag
+        id: tag
+        run: |
+          BASE="${{ steps.mod_info.outputs.name }}-${{ steps.mod_info.outputs.version }}"
+          TAG="$BASE"
+          i=1
+          while gh release view "$TAG" >/dev/null 2>&1; do
+            TAG="${BASE}($i)"
+            i=$((i+1))
+          done
+          echo "tag=$TAG" >> $GITHUB_OUTPUT
+
+      - name: Create release
+        uses: softprops/action-gh-release@v1
+        with:
+          tag_name: ${{ steps.tag.outputs.tag }}
+          name: ${{ steps.tag.outputs.tag }}
+        env:
+          GITHUB_TOKEN: ${{ secrets.GH_TOKEN }}
+
+      - name: Upload jar to release
+        uses: softprops/action-gh-release@v1
+        with:
+          tag_name: ${{ steps.tag.outputs.tag }}
+          files: ./release-artifacts/*.jar
+        env:
+          GITHUB_TOKEN: ${{ secrets.GH_TOKEN }}