Setting for passkey default group

### Checks

- [x] I have read the Wiki, searched the open issues, and still think this is a new feature.

### Explain the problem clearly and succinctly:

At present, it is only possible to save Passkey entries manually.

### Describe the solution you'd like:

It is possible to save them automatically if a group is predefined. This parameter should be saved per database.

### Describe alternatives you've considered:

_No response_

### Additional context:

_No response_

The issue does not name files or tests. Start by locating the passkey save flow and the existing per-database settings, then trace how group selection is stored; done means a predefined group automatically receives saved passkeys and the setting persists separately for each database.

Written by the indexing model from the issue text.