fix(apple/tvOS): system-style slide for in-stack pushes (swiftui-navigation-transitions)

SwiftUI's NavigationStack on tvOS animates pushes as a bare crossfade with no public
customization — the system Settings app slides. The home stack now applies
.customNavigationTransition(.slide) on tvOS via davdroman/swiftui-navigation-transitions
(MIT, tvOS 13+), covering the top-level routes AND the settings pickers' drill-ins.

The dependency is referenced by the Xcode PROJECT only and linked solely by the
Punktfunk-tvOS target: its manifest (no macOS platform declared vs 10.15 deps) breaks
SwiftPM whole-graph validation for plain `swift build`, and the #if os(tvOS) import
never compiles in the macOS-only SwiftPM dev shell anyway. Headless builds need
xcodebuild -skipMacroValidation (the lib pulls Swift macro packages; in the Xcode UI
it's a one-time Trust & Enable prompt).

iOS/macOS keep their untouched system navigation animations.

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

clients/apple/Sources/PunktfunkClient/ContentView.swift

@@ -13,6 +13,9 @@ import AppKit
 #endif
 import PunktfunkKit
 import SwiftUI
+#if os(tvOS)
+import SwiftUINavigationTransitions
+#endif
 
 struct ContentView: View {
     @StateObject private var model = SessionModel()
@@ -181,6 +184,11 @@ struct ContentView: View {
         #if os(macOS)
         .frame(minWidth: 480, minHeight: 360)
         #endif
+        #if os(tvOS)
+        // The Settings-app slide for every push in this stack (top-level routes AND
+        // the pickers' drill-ins) — SwiftUI's default on tvOS is a bare crossfade.
+        .customNavigationTransition(.slide)
+        #endif
         #if !os(tvOS)
         .sheet(isPresented: $showAddHost) {
             AddHostSheet { store.add($0) }