Add application, Dockerfile, CI workflow and documentation

- FastAPI-based Matrix chat export tool with E2E support
- Dockerfile with Python 3.12-slim base image
- Docker Compose with dedicated network configuration
- Gitea Actions workflow for automated image builds
- README with setup instructions and feature overview
- MIT license

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

.gitea/workflows/docker-publish.yml

@@ -0,0 +1,38 @@
+name: Build & Push Docker Image
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v4
+
+      - name: Version aus Tag extrahieren
+        id: version
+        run: |
+          VERSION=$(echo "${{ gitea.ref_name }}" | sed 's/^v//')
+          echo "VERSION=$VERSION" >> $GITHUB_OUTPUT
+
+      - name: Bei Registry einloggen
+        run: |
+          echo "${{ secrets.REGISTRY_TOKEN }}" | \
+          docker login ${{ vars.REGISTRY_URL }} \
+          --username "${{ secrets.REGISTRY_USER }}" \
+          --password-stdin
+
+      - name: Docker Image bauen
+        run: |
+          docker build \
+          -t ${{ vars.REGISTRY_URL }}/${{ gitea.repository }}:${{ steps.version.outputs.VERSION }} \
+          -t ${{ vars.REGISTRY_URL }}/${{ gitea.repository }}:latest \
+          .
+
+      - name: Docker Image pushen
+        run: |
+          docker push ${{ vars.REGISTRY_URL }}/${{ gitea.repository }}:${{ steps.version.outputs.VERSION }}
+          docker push ${{ vars.REGISTRY_URL }}/${{ gitea.repository }}:latest