ci: build and tag images for all branches

- Trigger build on all branches (not only main)
- Tag image as 'latest' for main, branch name otherwise
- Sanitize branch name for Docker tag (slashes → dashes, lowercase)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -3,24 +3,45 @@ name: Build and Push Multi-Platform Images
 on:
   push:
     branches:
-      - main
+      - "**"
 
 jobs:
   build-and-push:
     runs-on: ubuntu-latest
+
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
 
+      - name: Set image tag
+        id: vars
+        run: |
+          BRANCH_NAME="${GITHUB_REF_NAME}"
+
+          # Docker-Tags dürfen z. B. keine Slashes enthalten
+          SAFE_BRANCH_NAME=$(echo "$BRANCH_NAME" | tr '/' '-' | tr '[:upper:]' '[:lower:]')
+
+          if [ "$BRANCH_NAME" = "main" ]; then
+            echo "tag=latest" >> "$GITHUB_OUTPUT"
+          else
+            echo "tag=$SAFE_BRANCH_NAME" >> "$GITHUB_OUTPUT"
+          fi
+
       - name: Login to Gitea Container Registry
         run: echo "${{ secrets.REGISTRY_TOKEN }}" | docker login gitea.poettker-cloud.de -u "${{ gitea.actor }}" --password-stdin
 
       - name: Build and Push Backend
         run: |
-          docker build -t gitea.poettker-cloud.de/bjoernpoettker/paperlessmanager-backend:latest ./paperless-backend
-          docker push gitea.poettker-cloud.de/bjoernpoettker/paperlessmanager-backend:latest
+          docker build \
+            -t gitea.poettker-cloud.de/bjoernpoettker/paperlessmanager-backend:${{ steps.vars.outputs.tag }} \
+            ./paperless-backend
+
+          docker push gitea.poettker-cloud.de/bjoernpoettker/paperlessmanager-backend:${{ steps.vars.outputs.tag }}
 
       - name: Build and Push Frontend
         run: |
-          docker build -t gitea.poettker-cloud.de/bjoernpoettker/paperlessmanager-frontend:latest ./paperless-frontend
-          docker push gitea.poettker-cloud.de/bjoernpoettker/paperlessmanager-frontend:latest
+          docker build \
+            -t gitea.poettker-cloud.de/bjoernpoettker/paperlessmanager-frontend:${{ steps.vars.outputs.tag }} \
+            ./paperless-frontend
+
+          docker push gitea.poettker-cloud.de/bjoernpoettker/paperlessmanager-frontend:${{ steps.vars.outputs.tag }}