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/PairSheet.swift

@@ -44,9 +44,6 @@ struct PairSheet: View {
     var body: some View {
         #if os(tvOS)
         VStack(spacing: 24) {
-            Label("Pair with \(host.displayName)", systemImage: "lock.shield")
-                .font(.title3.weight(.semibold))
-                .foregroundStyle(.tint)
             Text("The host prints the PIN when pairing is armed "
                 + "(--allow-pairing, \u{201C}PAIRING ARMED\u{201D} in its log). "
                 + "Pairing verifies both sides at once — no fingerprint comparison "
@@ -80,6 +77,7 @@ struct PairSheet: View {
         }
         .frame(maxWidth: 1000)
         .padding(60)
+        .navigationTitle("Pair with \(host.displayName)")
         .onDisappear { token.cancelled = true }
         .fullScreenCover(item: $editing) { field in
             switch field {