CI: Ergaenzt Nightly-Docker-Image in nightly.yaml

- Baut und veroeffentlicht bei Aenderungen auf nightly zusaetzlich zu den
  Debian/RPM/Arch-Paketen ein Docker-Container-Image, analog zu den
  Testing-/Stable-Docker-Steps in testing.yaml/main.yaml.
- Tags: nightly, <VERSION>-nightly, <VERSION>-nightly.<BUILD_NUMBER>,
  nightly-<BUILD_NUMBER>.
- 'Dockerfile' zum Change-Filter der nightly.yaml ergaenzt, damit reine
  Dockerfile-Aenderungen ebenfalls einen Nightly-Build ausloesen.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitea/workflows/nightly.yaml

@@ -26,6 +26,7 @@ jobs:
               - 'Cargo.lock'
               - 'scripts/**'
               - '.cargo/**'
+              - 'Dockerfile'
               - '.gitea/workflows/nightly.yaml'
 
   build-and-publish:
@@ -169,3 +170,34 @@ jobs:
               --upload-file "$pkg" \
               "${GITEA_URL}/api/packages/${REPO_OWNER}/arch/nightly"
           done
+
+      - name: Build and Publish Docker Container Image (Nightly)
+        env:
+          GITEA_URL: ${{ gitea.server_url || github.server_url }}
+          REPO: ${{ gitea.repository || github.repository }}
+          REPO_OWNER: ${{ gitea.repository_owner || github.repository_owner }}
+          REPO_NAME: ${{ gitea.repository_name || github.event.repository.name }}
+          TOKEN: ${{ secrets.PACKAGE_TOKEN || secrets.RELEASE_TOKEN || secrets.PUBLISH_TOKEN || secrets.API_TOKEN || secrets.PAT_TOKEN || secrets.CUSTOM_TOKEN || secrets.GITEA_TOKEN || secrets.GITHUB_TOKEN || github.token }}
+        run: |
+          VERSION="$(sed -n 's/^version = "\(.*\)"/\1/p' Cargo.toml | head -n1)"
+          REGISTRY_HOST=$(echo "${GITEA_URL}" | sed -E 's|^https?://||; s|/.*$||')
+          IMAGE_NAME=$(echo "${REGISTRY_HOST}/${REPO_OWNER}/${REPO_NAME}" | tr '[:upper:]' '[:lower:]')
+
+          echo "Authentifiziere an der Container Registry ${REGISTRY_HOST}..."
+          echo "${TOKEN}" | docker login "${REGISTRY_HOST}" -u "${REPO_OWNER}" --password-stdin
+
+          echo "Baue Docker-Container Image (Nightly)..."
+          docker build \
+            --build-arg TARGET_BIN=target/x86_64-unknown-linux-gnu/release/mirror-package \
+            -t "${IMAGE_NAME}:nightly" \
+            -t "${IMAGE_NAME}:${VERSION}-nightly" \
+            -t "${IMAGE_NAME}:${VERSION}-nightly.${BUILD_NUMBER}" \
+            -t "${IMAGE_NAME}:nightly-${BUILD_NUMBER}" \
+            .
+
+          echo "Veröffentliche Docker-Images nach ${IMAGE_NAME}..."
+          docker push "${IMAGE_NAME}:nightly"
+          docker push "${IMAGE_NAME}:${VERSION}-nightly"
+          docker push "${IMAGE_NAME}:${VERSION}-nightly.${BUILD_NUMBER}"
+          docker push "${IMAGE_NAME}:nightly-${BUILD_NUMBER}"
+          echo "Docker-Images (Nightly) erfolgreich veröffentlicht."