Why
===

More holds a tab's root and the routes above it once a row of its list is picked. When the app replaced that root (a fresh entry, as `open` makes for another URL), the old root's node left the tree, so `moreTab`, which names the tab of More's first route by the tabpanel holding its node, named none. `syncTabs` then wrote the new root into the tab's own controller while More still showed the old one.

How
===

Each route's controller records the tabpanel it was last projected from (`RouteController.panel`), and `tabIndex(ofRoute:)` falls back to it once the route's node has left the tree. `moreTab` then names the tab while More holds its replaced root, and the sync writes the new root into More, where UIKit holds the tab's routes. `followMore`, `followSelection` and `declineMoreRow` read the same lookup through `tabIndex(ofShown:)`, so they too map a route More shows that the app replaced or removed to its tab. `NavigationMoreIOSTests.testATabsNewRootIsWrittenIntoMoreWhileMoreHoldsTheOldOne` opens Five at another URL from its root under More (the More fixture's Renew) and checks that More shows the new root and Five's own controller holds none of its routes.

Test Plan
===

With this change on `main` `1229a5be4c`, on an iPhone 18 Pro simulator (iOS 27.0), `NavigationMoreIOSTests`, `NavigationSequenceIOSTests`, `NavigationPopIOSTests`, `UIKitTabFactsIOSTests`, `NavigationTabsIOSTests`, `TabStacksIOSTests` and `TabsIOSTests` pass bare and hosted, run through `xcodebuild test-without-building` with the run files, fixture environment and accessibility setting `bun host/apple/build.mjs --test --ios` gives them. `NavigationTabsIOSTests.testSharePresentsOverAnAppOwnedTabContainer` is left out: on this simulator it has hung in `UIActivityViewController`'s presentation, waiting for `sharingd`. The iPad sidebar case and the height-only size class case skip on the iPhone. Without the fallback, `testATabsNewRootIsWrittenIntoMoreWhileMoreHoldsTheOldOne` fails: More holds the old root, and Five's own controller holds the new one. `bun host/apple/build.mjs --tvos --no-install` compiles, and `bun scripts/caps.mjs` passes.