Fix main navigation bar gestures like scroll to top not working on iOS 26

[patrys]

Liquid glass takes over the tap gestures and the previously used double tap gesture is never triggered. This change replaces it with handling of tab re-selection inside the tabBarController(_:didSelect:) delegate.

Fixes #1530

[CLAassistant]

All committers have signed the CLA.

[patrys]

One regression that is not easy to work around is that in didSelect it's hard to tell if any views were popped from the view stack. Which means if you scroll down, load a post, and then tap Home, you will not only navigate back out of the post but also scroll to the top, which is annoying (but still better than not having a way to scroll to the top).

[patrys]

Actually, scratch the above, the original implementation suffered from the same compromise.

[whattherestimefor]

Since the previous solution was implemented with a double tap gesture, how about adding a timing check to this one so that the reselection has to be close in time (probably < 0.5 sec) to the previous one, to avoid too many accidental triggers?

[patrys]

@whattherestimefor Did you have a chance to test this on device? I'm not sure it's worth adding a delay since it seems to do some sort of internal debouncing, at least on iOS 26.

We can also later replace the UITabBar with a SwiftUI TabView, which handles this automatically when the tab contains a scroll view.