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/vite.config.ts

@@ -1,8 +1,17 @@
 import { defineConfig } from 'vite';
 import react from '@vitejs/plugin-react';
+import { readFileSync } from 'node:fs';
+
+// Shown in the header. Release builds get the git tag (APP_VERSION build argument, e.g. "v0.2");
+// other builds show the package version with a "-dev" suffix.
+const pkg = JSON.parse(readFileSync(new URL('./package.json', import.meta.url), 'utf8'));
+const appVersion = process.env.APP_VERSION || `v${pkg.version.replace(/\.0$/, '')}-dev`;
 
 export default defineConfig({
   plugins: [react()],
+  define: {
+    __APP_VERSION__: JSON.stringify(appVersion),
+  },
   server: {
     port: 5173,
     proxy: {