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/SettingsView.swift

@@ -87,9 +87,6 @@ struct SettingsView: View {
                     .font(.caption)
                     .foregroundStyle(.secondary)
             }
-            Section {
-                Button("Done") { dismiss() }
-            }
         }
         .navigationTitle("Settings")
     }