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>

frontend/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "mindsift-frontend",
-  "version": "1.0.0",
+  "version": "0.2.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "mindsift-frontend",
-      "version": "1.0.0",
+      "version": "0.2.0",
       "dependencies": {
         "@types/prismjs": "^1.26.6",
         "framer-motion": "^11.15.0",