fix(apple/tvOS): pushed routes instead of modal covers — the Settings-app navigation feel

Add Host, Settings and PIN pairing were fullScreenCover overlays, which is why
navigating felt unlike the system Settings app (no push animation, no Menu-pops-a-level
semantics). They are now navigationDestination ROUTES pushed inside the home
NavigationStack:

- the system push/pop animation and Menu-button back navigation come for free;
- the Settings pickers' navigationLink pushes reuse the same stack (its inner
  NavigationStack wrapper is gone, as is the tvOS Done row — Menu pops, like Settings);
- Add Host is a real full-screen page (system navigation title, Settings-style rows on
  the standard backdrop) instead of a floating dialog, same for the pairing page;
- the thickMaterial cover backdrops became unnecessary and are gone. The system
  keyboard entries stay as covers — that presentation is system-owned either way.

iOS/macOS keep their sheets. Verified by screenshot: Add Host renders as a pushed
full-screen route with the title top-center.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/apple/Sources/PunktfunkClient/AddHostSheet.swift

@@ -23,8 +23,6 @@ struct AddHostSheet: View {
         // No inline text editing on tvOS — Settings-style value rows; pressing one
         // raises the SYSTEM fullscreen keyboard (TVTextEntry).
         VStack(spacing: 24) {
-            Text("Add Host")
-                .font(.title3.weight(.semibold))
             TVFieldRow(
                 label: "Name", value: name, placeholder: "Optional"
             ) { editing = .name }
@@ -43,6 +41,7 @@ struct AddHostSheet: View {
         }
         .frame(maxWidth: 1000)
         .padding(60)
+        .navigationTitle("Add Host")
         .fullScreenCover(item: $editing) { field in
             switch field {
             case .name: