add artifact merge job to combine all platform builds

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: electronstudio

.github/workflows/build.yml

@@ -258,4 +258,26 @@ jobs:
         uses: actions/upload-artifact@v4
         with:
           name: jaylib-windows-x86
-          path: ./jaylib-natives*.jar
+          path: ./jaylib-natives*.jar
+
+  merge-artifacts:
+    runs-on: ubuntu-latest
+    needs: [build-linux, build-linux-32bit, build-mac, build-windows, build-windows32]
+    
+    steps:
+      - name: Download all artifacts
+        uses: actions/download-artifact@v4
+        with:
+          path: artifacts
+          merge-multiple: true
+      
+      - name: Create merged artifact
+        run: |
+          cd artifacts
+          zip -r ../jaylib-all-platforms.zip .
+      
+      - name: Upload merged artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: jaylib-all-platforms
+          path: jaylib-all-platforms.zip