Make Docker build optional in Gitea Actions workflow

- Check if Docker is available before attempting to use it
- Skip Docker image builds gracefully if Docker is not installed
- Provide helpful instructions for enabling Docker support
- Add error handling for Docker build failures
- Allow workflow to succeed even without Docker
- Binary builds will still complete successfully

.gitea/workflows/release.yml

@@ -158,10 +158,17 @@ jobs:
             git checkout -b ${{ github.ref_name }} origin/${{ github.ref_name }}
           fi
 
-      - name: Set up Docker
+      - name: Check Docker availability
         run: |
+          if ! command -v docker &> /dev/null; then
+            echo "⚠️  Docker is not available on this runner"
+            echo "Docker images will not be built. To enable Docker builds:"
+            echo "1. Install Docker on the runner machine"
+            echo "2. Ensure the runner has permission to use Docker"
+            echo "See GITEA_SETUP.md for more information"
+            exit 0
+          fi
           docker --version
-          which docker
 
       - name: Generate version
         id: version
@@ -175,22 +182,46 @@ jobs:
 
       - name: Build Docker images
         run: |
+          if ! command -v docker &> /dev/null; then
+            echo "Docker not available, skipping Docker image build"
+            exit 0
+          fi
+          
           mkdir -p /tmp/docker-images
           
           echo "Building server image..."
           docker build -t nerd-monitor-server:${{ env.version }} -f Dockerfile.server .
-          docker save nerd-monitor-server:${{ env.version }} -o /tmp/docker-images/nerd-monitor-server-${{ env.version }}.tar
+          if [ $? -eq 0 ]; then
+            docker save nerd-monitor-server:${{ env.version }} -o /tmp/docker-images/nerd-monitor-server-${{ env.version }}.tar
+            echo "✓ Server image built and saved"
+          else
+            echo "✗ Failed to build server image"
+            exit 1
+          fi
           
           echo "Building agent image..."
           docker build -t nerd-monitor-agent:${{ env.version }} -f Dockerfile.agent .
-          docker save nerd-monitor-agent:${{ env.version }} -o /tmp/docker-images/nerd-monitor-agent-${{ env.version }}.tar
+          if [ $? -eq 0 ]; then
+            docker save nerd-monitor-agent:${{ env.version }} -o /tmp/docker-images/nerd-monitor-agent-${{ env.version }}.tar
+            echo "✓ Agent image built and saved"
+          else
+            echo "✗ Failed to build agent image"
+            exit 1
+          fi
           
+          echo ""
           echo "Docker images built:"
           ls -lh /tmp/docker-images/
 
       - name: Upload Docker images to release
         if: startsWith(github.ref, 'refs/tags/')
         run: |
+          # Skip if no Docker images were built
+          if [ ! -d /tmp/docker-images ] || [ -z "$(ls -A /tmp/docker-images/)" ]; then
+            echo "No Docker images to upload (Docker not available on runner)"
+            exit 0
+          fi
+          
           export GITEA_TOKEN="${{ secrets.GITEA_TOKEN }}"
           export GITEA_URL="${{ github.server_url }}"
           export REPO_OWNER="${{ github.repository_owner }}"