Fetching - Summaries / Emails

### Frontend
In the pursuit of fixing summaries mapping to emails In the inbox view correctly, re-evaluate and clarify fetching strategy.
Similar to initial 5 summary fetch, avoid huge batches unless properly handling the rendering/mapping of summaries to their respective emails in inbox view.

### Backend
Ensure /fetch/{id} and /fetch/{id,id,..} is working as intended for /emails/ and /summaries/