feat(frontend): add editor integration shell and draft read-model views

- add editor integration shell
- add editor context read flow
- add draft flow entry handling
- add summary, structure, validation and compare-preview views
- render backend read models for draft and published states
- verify sample-contract entities: 3 seats, 1 group, 1 sector

.env.example

@@ -1,4 +1,4 @@
 VITE_FRONTEND_PORT=28080
-VITE_APP_TITLE=SVG Service Admin UI
+VITE_APP_TITLE=SVG Service Frontend
 VITE_API_BASE_URL=http://127.0.0.1:9020
 VITE_API_KEY=admin-local-dev-key