feat(backend): add editor context, draft bootstrap flow and draft summary endpoints

- add editor context endpoint for published and draft state introspection
- add ensure-draft endpoint to create or reuse the current editable draft
- add draft summary endpoint with validation, diff and publish readiness summary
- align draft read endpoints with optimistic concurrency via expected_scheme_version_id
- fix startup, import and schema issues in editor entry flow
- update smoke regression coverage for editor entry flow

backend/app/api/routes/editor.py

@@ -170,7 +170,7 @@ async def get_draft_summary(
     readiness = await build_publish_readiness(
         scheme_id=scheme.scheme_id,
         scheme_version_id=version.scheme_version_id,
-        status=version.status,
+       status=version.status,
     )
 
     return DraftSummaryResponse(