Add optimized Gitea CI/CD workflows for Docker builds

Features:
- docker-autobuild.yaml: Automated builds on push to main/master
  - Path ignores for markdown/docs files
  - Docker Buildx with caching support
  - Automatic cleanup after builds

- docker-build.yaml: Manual builds with flexible options
  - Custom version tags
  - Additional tags support (e.g., stable,production)
  - Toggle latest tag
  - Docker Buildx with layer caching

Both workflows:
- Use registry credentials from Gitea secrets
- Support local registry at 192.168.88.201:5000
- Proper login/logout handling
- Optimized for sticker-bot project

.gitea/workflows/docker-autobuild.yaml

@@ -0,0 +1,63 @@
+name: Auto Build and Push Docker Image
+
+on:
+  push:
+    branches:
+      - main
+      - master
+    paths-ignore:
+      - '**.md'
+      - '.gitignore'
+      - 'data/**'
+      - '.env.example'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Docker Registry
+        run: |
+          echo "${{ secrets.REGISTRY_PASSWORD }}" | docker login -u "${{ secrets.REGISTRY_USERNAME }}" --password-stdin 192.168.88.201:5000 || true
+
+      - name: Build and Push Docker Image
+        run: |
+          REGISTRY="192.168.88.201:5000"
+          IMAGE_NAME="${{ gitea.repository }}"
+          
+          # Versionierung: v{run_number}-autobuild
+          VERSION="v${{ gitea.run_number }}-autobuild"
+          FULL_IMAGE_PATH="$REGISTRY/$IMAGE_NAME"
+          
+          echo "========================================"
+          echo "Building Docker Image"
+          echo "Registry: $REGISTRY"
+          echo "Image: $IMAGE_NAME"
+          echo "Version: $VERSION"
+          echo "========================================"
+          
+          # Build with cache
+          docker build \
+            --cache-from $FULL_IMAGE_PATH:latest \
+            -t $FULL_IMAGE_PATH:latest \
+            -t $FULL_IMAGE_PATH:$VERSION \
+            .
+          
+          # Push images
+          docker push $FULL_IMAGE_PATH:latest
+          docker push $FULL_IMAGE_PATH:$VERSION
+          
+          echo "✅ Successfully built and pushed:"
+          echo "  - $FULL_IMAGE_PATH:latest"
+          echo "  - $FULL_IMAGE_PATH:$VERSION"
+
+      - name: Cleanup
+        if: always()
+        run: |
+          docker logout 192.168.88.201:5000 || true
+          docker system prune -f || true