release: v0.2 – collaboration docs, richer demo data, new screenshots

- Turn the collaboration plan into module docs (Doku/modules/collaboration.md)
  describing the implemented state; remove Doku/plans
- Header version comes from the build: git tag via APP_VERSION (CI passes
  it for tag builds), otherwise "<package version>-dev"; package 0.2.0
- Sample data (setup option and demo mode): six inbox thoughts, two task
  lists with Kanban states, subtasks and due dates, shopping and packing
  lists, three notes in folders incl. a long nested outline; demo mode
  shares the note and two lists with user/user
- e2e/screenshots.sh renews the README screenshots from demo data
- README: live collaboration, editor sharing, image tags, version badge

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/build-and-publish.yaml

@@ -37,6 +37,12 @@ jobs:
           echo "image=${IMAGE_NAME}" >> "$GITHUB_OUTPUT"
           echo "tag=${DOCKER_TAG}" >> "$GITHUB_OUTPUT"
           echo "actor=${ACTOR_NAME}" >> "$GITHUB_OUTPUT"
+          # Releases (tags) show the tag as version in the app header
+          APP_VERSION=""
+          case "${GITHUB_REF:-}" in
+            refs/tags/*) APP_VERSION="${REF_NAME}" ;;
+          esac
+          echo "app_version=${APP_VERSION}" >> "$GITHUB_OUTPUT"
           echo "Target Docker image: ${IMAGE_NAME}:${DOCKER_TAG} (Registry: ${REGISTRY_HOST}, Actor: ${ACTOR_NAME})"
 
       - name: Login to Gitea Container Registry
@@ -50,6 +56,6 @@ jobs:
         run: |
           FULL_IMAGE="${{ steps.prep.outputs.image }}:${{ steps.prep.outputs.tag }}"
           echo "🚀 Building container & executing Frontend/Backend checks inside image: ${FULL_IMAGE}"
-          DOCKER_BUILDKIT=1 docker build --progress=plain -t "${FULL_IMAGE}" .
+          DOCKER_BUILDKIT=1 docker build --progress=plain --build-arg APP_VERSION="${{ steps.prep.outputs.app_version }}" -t "${FULL_IMAGE}" .
           echo "✅ All checks & tests passed inside container! Pushing ${FULL_IMAGE}..."
           docker push "${FULL_IMAGE}"