Add Save button to SettingsView

Add save button to top right that user would press to 'accept' changes to lat / long values.

If not pressed, then changes to lat / long are not saved on back button click and return to Navigation View.

Start by locating SettingsView and its navigation back-button handling, then trace how latitude and longitude changes are currently stored. Add a top-right Save action that commits those changes, while leaving back navigation without saving when it is not pressed. Verify both save and back-without-save behavior when returning to Navigation View.

Written by the indexing model from the issue text.