Back button appears to move around and is confusingly labelled

## What Happened

To go back to the previous choice, you sometimes have to press a button marked "Back" at the bottom of the window but when choosing a language or keyboard variant you can press a button at the top of the list there may or may not be a "Back" button in these circumstances. This is confusing. It is also not always clear where the "Back" button will return to.

## Expected Behavior

There should be a way of going back to the previous choice that is clear and consistent for non-technical users.

## Steps to Reproduce

1. Start `io.elementary.initial-setup` in Terminal
2. Click on "English..." in the list
3. To go back you need to press "Languages" at the top of the list of variants
4. Click on "United Kingdom" in the variant list
5. The keyboard layout list appears with a "Back" button at the bottom.
6. Press "Back". The "Back" button disappears and you have to go up to press "Languages" to go back further.
7. Return to the Keyboard layout list and click on "English (UK)..."
8. A list of keyboard variants shows. There are *two* "back" buttons one at the top marked "Input Language" (??) and one at the bottom just marked "Back"
9. Press "Back". The list of language variants shows (??) This is unexpected.

### Logs

## Platform Information

Elementary 6 daily

Start by running `io.elementary.initial-setup` and reproduce the language and keyboard navigation described in the issue. Trace the entry points responsible for the top and bottom navigation labels, then verify that each back action has one consistent location, label, and destination across the listed flows.

Written by the indexing model from the issue text.