Gallery doesn't close on back button when no internal navigation in the history stack

[maraf]

1. Open timeline
2. Open media in gallery
3. Press back button

In entry detail (possibly all detail pages), press back prevents the navigation and instead closes the gallery.

[maraf]

I dug into why the gallery behaves differently on timeline vs. entry detail.

NavigationLock only intercepts internal Blazor navigations. It does not react just because the PhotoSwipe gallery is open.

That means:

• On EntryDetail, Back usually works because the user typically came from another in-app page (/ -> /entries/{id}), so pressing Back attempts an internal route change and NavigationLock closes the gallery instead.
• On the timeline, opening the gallery is only a JS lightbox action on the same URL. No route change happens and no gallery-specific history entry is created. In that case, Back may try to leave the current document/history entry, so OnBeforeInternalNavigation is never invoked.
• The same limitation can also affect EntryDetail if it was opened directly and there is no previous in-app history entry.

So the issue is not timeline-specific in principle; timeline just hits it more reliably because opening the gallery there currently does not add any history step of its own.

The subtle fix is to add a lightweight same-URL history marker when the gallery opens, so the first Back action is consumed by closing the gallery.