Save 2FA sessions

### Describe the problem

Having to log-in very often due to short sessions is uncomfortable with password manager and passkeys alike, but needing to insert an OTP every time is annoying.

### Solution brainstorm

It would be great to enable saving a session (use "_save this browser for # days_" wording) with a checkbox next to the OTP field for some period of time (like 30 or 60 days), to prevent asking the user for OTP too often. Many services have that; it should not lower security much.

### Describe alternatives you have considered

_No response_

### Screenshots

_No response_

### Additional context

It would be great to implement the following two related issues as well while working on this:

- https://github.com/WeblateOrg/weblate/issues/12250
- https://github.com/WeblateOrg/weblate/issues/16431

No files, tests, or entry points are named. Start by reviewing related issues #12250 and #16431, then trace the existing OTP and session flow; done should include an option beside the OTP field to remember the browser for a defined period such as 30 or 60 days.

Written by the indexing model from the issue text.