feat: implement MeshtasticNavDisplay and centralize Navigation 3 configuration

- Introduce `MeshtasticNavDisplay` in `core:ui` to encapsulate shared Navigation 3 configuration, including entry decorators, scene strategies, and transitions.
- Integrate `rememberViewModelStoreNavEntryDecorator` to provide entry-scoped `ViewModelStoreOwner` support, ensuring ViewModels are automatically cleared when their backstack entry is popped.
- Configure `DialogSceneStrategy` to enable navigation-driven dialogs that respect backstack lifecycle and predictive back gestures.
- Implement a standardized 350 ms crossfade transition for both forward and pop navigation across all platforms.
- Refactor `app` and `desktop` host modules to utilize `MeshtasticNavDisplay`, removing redundant manual configuration of `NavDisplay` and decorators.
- Update `core:ui` dependencies to include `lifecycle-viewmodel-navigation3` and move it away from platform-specific host modules.
- Update architectural documentation (`AGENTS.md`, `GEMINI.md`, and decision logs) to reflect the adoption of centralized navigation and ViewModel scoping patterns.

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

@@ -24,22 +24,20 @@ 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
+import org.meshtastic.core.ui.component.MeshtasticNavDisplay
 import org.meshtastic.core.ui.viewmodel.UIViewModel
 import org.meshtastic.desktop.navigation.desktopNavGraph
 
 /**
- * Desktop main screen — Navigation 3 shell with a persistent [NavigationRail] and [NavDisplay].
+ * Desktop main screen — Navigation 3 shell with a persistent [NavigationRail] and shared [MeshtasticNavDisplay].
  *
- * Uses the same shared routes from `core:navigation` and the same `NavDisplay` + `entryProvider` pattern as the Android
- * app, proving the shared backstack architecture works across targets.
+ * Uses the same shared routes from `core:navigation` and the same `MeshtasticNavDisplay` + `entryProvider` pattern as
+ * the Android app, proving the shared backstack architecture works across targets.
  */
 @Composable
 @Suppress("LongMethod")
@@ -56,17 +54,7 @@ fun DesktopMainScreen(backStack: NavBackStack<NavKey>, uiViewModel: UIViewModel
             ) {
                 val provider = entryProvider<NavKey> { desktopNavGraph(backStack, uiViewModel) }
 
-                NavDisplay(
-                    backStack = backStack,
-                    onBack = { backStack.removeLastOrNull() },
-                    entryDecorators =
-                    listOf(
-                        rememberSaveableStateHolderNavEntryDecorator<NavKey>(),
-                        rememberViewModelStoreNavEntryDecorator<NavKey>(),
-                    ),
-                    entryProvider = provider,
-                    modifier = Modifier.fillMaxSize(),
-                )
+                MeshtasticNavDisplay(backStack = backStack, entryProvider = provider, modifier = Modifier.fillMaxSize())
             }
         }
     }