feat: upgrade to Navigation 3 Beta 01 and implement entry-scoped ViewModels

- Update Navigation 3 to `1.1.0-beta01`, JetBrains Lifecycle to `2.11.0-alpha02`, and Compose Multiplatform to `1.11.0-beta01`.
- Integrate `ViewModelStoreNavEntryDecorator` and `SaveableStateHolderNavEntryDecorator` into `NavDisplay` for both Android and Desktop shells.
- Enable automatic ViewModel scoping where ViewModels obtained via `koinViewModel()` inside `entry<T>` blocks are now tied to the backstack entry's lifetime and cleared on pop.
- Add `jetbrains.lifecycle.viewmodel.navigation3` dependency to support entry-level `ViewModelStore` management.
- Update `AGENTS.md`, `GEMINI.md`, and `copilot-instructions.md` to reflect the transition from Activity/Window-scoped ViewModels to entry-scoped lifecycles.
- Introduce `navigation3-api-alignment-2026-03.md` to document the audit of Navigation 3 Scene architecture and Material 3 Adaptive integration.
- Update `kmp-status.md` and existing decision docs to reflect the new dependency baseline and predictive back handling via `NavigationBackHandler`.

desktop/src/main/kotlin/org/meshtastic/desktop/ui/DesktopMainScreen.kt

@@ -24,9 +24,11 @@ import androidx.compose.material3.Surface
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.dp
+import androidx.lifecycle.viewmodel.navigation3.rememberViewModelStoreNavEntryDecorator
 import androidx.navigation3.runtime.NavBackStack
 import androidx.navigation3.runtime.NavKey
 import androidx.navigation3.runtime.entryProvider
+import androidx.navigation3.runtime.rememberSaveableStateHolderNavEntryDecorator
 import androidx.navigation3.ui.NavDisplay
 import org.koin.compose.viewmodel.koinViewModel
 import org.meshtastic.core.ui.component.MeshtasticAppShell
@@ -57,6 +59,11 @@ fun DesktopMainScreen(backStack: NavBackStack<NavKey>, uiViewModel: UIViewModel
                 NavDisplay(
                     backStack = backStack,
                     onBack = { backStack.removeLastOrNull() },
+                    entryDecorators =
+                    listOf(
+                        rememberSaveableStateHolderNavEntryDecorator<NavKey>(),
+                        rememberViewModelStoreNavEntryDecorator<NavKey>(),
+                    ),
                     entryProvider = provider,
                     modifier = Modifier.fillMaxSize(),
                 )