fix: cell-network name, install error surfacing, health history cleanup

- docker-compose.services.yml: change external network name from
  pic_cell-network to cell-network so store-service compose files can find
  it.  The project-prefixed name was overriding the explicit name: cell-network
  fix in docker-compose.yml when both files were merged by make start.

- service_store.py: normalize docker compose stderr into the error key in
  the 400 response so the Store page shows the actual failure reason instead
  of the generic fallback message.

- app.py: skip health checks for email/calendar/files managers when those
  optional store services are not installed — prevents false Down alerts and
  unnecessary noise in health history.

- Logs.jsx: remove Email/Calendar/Files columns from the health history table;
  they are optional store services, not core builtins that should always appear.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.services.yml

@@ -3,4 +3,4 @@ services: {}
 networks:
   cell-network:
     external: true
-    name: pic_cell-network
+    name: cell-network