Closes#3862
I refactored the settings code, removing `_settings_` from some function
names where it was redundant.
The log level is more difficult to change live, so I added a
`tracing::info!` noting that it will apply on next app start.
```[tasklist]
### Before merging
- [x] Document whether pressing Enter on a field to apply settings is intended behavior
- [x] Document that log levels don't apply until next app start
- [x] Document that auth and API URL apply on next sign-in
```
