ci: add manual build workflow with custom image tag

New workflow_dispatch workflow to build & push backend/frontend images
with a manually chosen tag and service selection (both/backend/frontend).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/manual-build.yml

@@ -0,0 +1,53 @@
+name: Manual Build and Push (custom tag)
+
+on:
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: "Container-Tag (z. B. stable, v1.2.3, hotfix)"
+        required: true
+        default: "stable"
+      service:
+        description: "Welche Images bauen?"
+        type: choice
+        required: true
+        default: "both"
+        options:
+          - both
+          - backend
+          - frontend
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Show selected inputs
+        run: |
+          echo "Tag:     ${{ inputs.tag }}"
+          echo "Service: ${{ inputs.service }}"
+          echo "Ref:     ${{ github.ref_name }}"
+
+      - name: Login to Gitea Container Registry
+        run: echo "${{ secrets.REGISTRY_TOKEN }}" | docker login gitea.poettker-cloud.de -u "${{ gitea.actor }}" --password-stdin
+
+      - name: Build and Push Backend
+        if: ${{ inputs.service == 'both' || inputs.service == 'backend' }}
+        env:
+          TAG: ${{ inputs.tag }}
+        run: |
+          IMAGE="gitea.poettker-cloud.de/bjoernpoettker/paperlessmanager-backend:${TAG}"
+          docker build -t "$IMAGE" ./paperless-backend
+          docker push "$IMAGE"
+
+      - name: Build and Push Frontend
+        if: ${{ inputs.service == 'both' || inputs.service == 'frontend' }}
+        env:
+          TAG: ${{ inputs.tag }}
+        run: |
+          IMAGE="gitea.poettker-cloud.de/bjoernpoettker/paperlessmanager-frontend:${TAG}"
+          docker build -t "$IMAGE" ./paperless-frontend
+          docker push "$IMAGE"