Refactor newsletter generation and enhance user interface

- Update the newsletter generation logic to improve performance and maintainability.
- Revise the dashboard layout to streamline user interactions and enhance usability.
- Implement new input validation for newsletter fields to ensure data integrity.
- Adjust CSS styles for better visual consistency across the dashboard components.

.gitea/workflows/docker-build.yml

@@ -0,0 +1,57 @@
+name: Docker Image bauen & veröffentlichen
+
+on:
+  push:
+    branches:
+      - main
+    tags:
+      - "v*"
+  workflow_dispatch:
+
+env:
+  # Host der Gitea Container Registry (bei Bedarf als Repo-Variable REGISTRY überschreiben)
+  REGISTRY: ${{ vars.REGISTRY || 'git.hexahost.dev' }}
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Repository auschecken
+        uses: actions/checkout@v4
+
+      - name: Docker Buildx einrichten
+        uses: docker/setup-buildx-action@v3
+
+      - name: An Gitea Container Registry anmelden
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Metadaten (Tags & Labels) bestimmen
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=ref,event=branch
+            type=ref,event=tag
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=sha,format=short
+            type=raw,value=latest,enable={{is_default_branch}}
+
+      - name: Image bauen & pushen
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: ./Dockerfile
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}