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`.

app/src/main/kotlin/org/meshtastic/app/ui/Main.kt

@@ -26,10 +26,16 @@ import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.saveable.rememberSaveableStateHolder
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import androidx.lifecycle.viewmodel.compose.LocalViewModelStoreOwner
+import androidx.lifecycle.viewmodel.navigation3.ViewModelStoreNavEntryDecorator
+import androidx.lifecycle.viewmodel.navigation3.ViewModelStoreNavEntryDecoratorDefaults
 import androidx.navigation3.runtime.NavKey
+import androidx.navigation3.runtime.SaveableStateHolderNavEntryDecorator
 import androidx.navigation3.runtime.entryProvider
 import androidx.navigation3.runtime.rememberNavBackStack
 import androidx.navigation3.ui.NavDisplay
@@ -84,9 +90,24 @@ fun MainScreen(uIViewModel: UIViewModel = koinViewModel()) {
                     settingsGraph(backStack)
                     firmwareGraph(backStack)
                 }
+            val saveableStateHolder = rememberSaveableStateHolder()
+            val viewModelStoreOwner = checkNotNull(LocalViewModelStoreOwner.current)
+            val removeOnPop = ViewModelStoreNavEntryDecoratorDefaults.removeViewModelStoreOnPop()
             NavDisplay(
                 backStack = backStack,
                 entryProvider = provider,
+                entryDecorators =
+                listOf(
+                    remember(saveableStateHolder) {
+                        SaveableStateHolderNavEntryDecorator<NavKey>(saveableStateHolder)
+                    },
+                    remember(viewModelStoreOwner) {
+                        ViewModelStoreNavEntryDecorator<NavKey>(
+                            viewModelStore = viewModelStoreOwner.viewModelStore,
+                            removeViewModelStoreOnPop = removeOnPop,
+                        )
+                    },
+                ),
                 modifier = Modifier.fillMaxSize().recalculateWindowInsets().safeDrawingPadding(),
             )
         }