refactor: streamline main screen navigation and ViewModel injection

- Update `MainScreen` (Android) and `DesktopMainScreen` to manage their own `NavBackStack` initialization internally.
- Refactor `MainScreen` to obtain `UIViewModel` via Koin injection instead of receiving it as a parameter from `MainActivity`.
- Remove default bottom padding from `MeshtasticAppShell` and associated screen-level modifiers to allow for more flexible layout orchestration.
- Simplify `DesktopMainScreen` by moving backstack management inside the composable and cleaning up the navigation provider logic.
- Remove redundant lint suppressions in `Main.kt` following the simplification of the main screen composable structure.
- Clean up imports and normalize the usage of `MeshtasticNavDisplay` and `MeshtasticNavigationSuite` across platforms.

app/src/main/kotlin/org/meshtastic/app/MainActivity.kt

@@ -139,7 +139,7 @@ class MainActivity : ComponentActivity() {
                     ReportDrawnWhen { true }
 
                     if (appIntroCompleted) {
-                        MainScreen(uIViewModel = model)
+                        MainScreen()
                     } else {
                         val introViewModel = koinViewModel<IntroViewModel>()
                         AppIntroductionScreen(onDone = { model.onAppIntroCompleted() }, viewModel = introViewModel)

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

@@ -19,15 +19,12 @@
 package org.meshtastic.app.ui
 
 import androidx.compose.foundation.layout.fillMaxSize
-import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.recalculateWindowInsets
 import androidx.compose.foundation.layout.safeDrawingPadding
-import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.unit.dp
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.navigation3.runtime.NavKey
 import androidx.navigation3.runtime.entryProvider
@@ -43,6 +40,7 @@ import org.meshtastic.core.resources.app_too_old
 import org.meshtastic.core.resources.must_update
 import org.meshtastic.core.ui.component.MeshtasticAppShell
 import org.meshtastic.core.ui.component.MeshtasticNavDisplay
+import org.meshtastic.core.ui.component.MeshtasticNavigationSuite
 import org.meshtastic.core.ui.viewmodel.UIViewModel
 import org.meshtastic.feature.connections.navigation.connectionsGraph
 import org.meshtastic.feature.firmware.navigation.firmwareGraph
@@ -52,38 +50,36 @@ import org.meshtastic.feature.node.navigation.nodesGraph
 import org.meshtastic.feature.settings.navigation.settingsGraph
 import org.meshtastic.feature.settings.radio.channel.channelsGraph
 
-@OptIn(ExperimentalMaterial3Api::class)
-@Suppress("LongMethod", "CyclomaticComplexMethod")
 @Composable
-fun MainScreen(uIViewModel: UIViewModel = koinViewModel()) {
+fun MainScreen() {
+    val viewModel: UIViewModel = koinViewModel()
     val backStack = rememberNavBackStack(MeshtasticNavSavedStateConfig, NodesRoutes.NodesGraph as NavKey)
 
-    AndroidAppVersionCheck(uIViewModel)
+    AndroidAppVersionCheck(viewModel)
 
     MeshtasticAppShell(
         backStack = backStack,
-        uiViewModel = uIViewModel,
-        hostModifier = Modifier.safeDrawingPadding().padding(bottom = 16.dp),
+        uiViewModel = viewModel,
+        hostModifier = Modifier,
     ) {
-        org.meshtastic.core.ui.component.MeshtasticNavigationSuite(
+        MeshtasticNavigationSuite(
             backStack = backStack,
-            uiViewModel = uIViewModel,
+            uiViewModel = viewModel,
             modifier = Modifier.fillMaxSize(),
         ) {
-            val provider =
-                entryProvider<NavKey> {
-                    contactsGraph(backStack, uIViewModel.scrollToTopEventFlow)
-                    nodesGraph(
-                        backStack = backStack,
-                        scrollToTopEvents = uIViewModel.scrollToTopEventFlow,
-                        onHandleDeepLink = uIViewModel::handleDeepLink,
-                    )
-                    mapGraph(backStack)
-                    channelsGraph(backStack)
-                    connectionsGraph(backStack)
-                    settingsGraph(backStack)
-                    firmwareGraph(backStack)
-                }
+            val provider = entryProvider<NavKey> {
+                contactsGraph(backStack, viewModel.scrollToTopEventFlow)
+                nodesGraph(
+                    backStack = backStack,
+                    scrollToTopEvents = viewModel.scrollToTopEventFlow,
+                    onHandleDeepLink = viewModel::handleDeepLink,
+                )
+                mapGraph(backStack)
+                channelsGraph(backStack)
+                connectionsGraph(backStack)
+                settingsGraph(backStack)
+                firmwareGraph(backStack)
+            }
             MeshtasticNavDisplay(
                 backStack = backStack,
                 entryProvider = provider,
@@ -99,7 +95,6 @@ private fun AndroidAppVersionCheck(viewModel: UIViewModel) {
     val connectionState by viewModel.connectionState.collectAsStateWithLifecycle()
     val myNodeInfo by viewModel.myNodeInfo.collectAsStateWithLifecycle()
 
-    // Check if the device is running an old app version
     LaunchedEffect(connectionState, myNodeInfo) {
         if (connectionState == ConnectionState.Connected) {
             myNodeInfo?.let { info ->
@@ -120,4 +115,4 @@ private fun AndroidAppVersionCheck(viewModel: UIViewModel) {
             }
         }
     }
-}
+}

core/ui/src/commonMain/kotlin/org/meshtastic/core/ui/component/MeshtasticAppShell.kt

@@ -16,11 +16,9 @@
  */
 package org.meshtastic.core.ui.component
 
-import androidx.compose.foundation.layout.padding
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.unit.dp
 import androidx.navigation3.runtime.NavBackStack
 import androidx.navigation3.runtime.NavKey
 import org.meshtastic.core.navigation.NodeDetailRoutes
@@ -36,7 +34,7 @@ import org.meshtastic.core.ui.viewmodel.UIViewModel
 fun MeshtasticAppShell(
     backStack: NavBackStack<NavKey>,
     uiViewModel: UIViewModel,
-    hostModifier: Modifier = Modifier.padding(bottom = 16.dp),
+    hostModifier: Modifier = Modifier,
     content: @Composable () -> Unit,
 ) {
     LaunchedEffect(uiViewModel) {

desktop/src/main/kotlin/org/meshtastic/desktop/Main.kt

@@ -321,7 +321,7 @@ fun main(args: Array<String>) = application(exitProcessOnExit = false) {
             // re-reads Locale.current and all stringResource() calls update.  Unlike key(), this
             // preserves remembered state (including the navigation backstack).
             CompositionLocalProvider(LocalAppLocale provides localePref) {
-                AppTheme(darkTheme = isDarkTheme) { DesktopMainScreen(backStack) }
+                AppTheme(darkTheme = isDarkTheme) { DesktopMainScreen(uiViewModel) }
             }
         }
     }

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

@@ -18,41 +18,37 @@ package org.meshtastic.desktop.ui
 
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.padding
-import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.dp
-import androidx.navigation3.runtime.NavBackStack
 import androidx.navigation3.runtime.NavKey
 import androidx.navigation3.runtime.entryProvider
-import org.koin.compose.viewmodel.koinViewModel
+import org.meshtastic.core.navigation.MeshtasticNavSavedStateConfig
+import org.meshtastic.core.navigation.NodesRoutes
 import org.meshtastic.core.ui.component.MeshtasticAppShell
 import org.meshtastic.core.ui.component.MeshtasticNavDisplay
+import org.meshtastic.core.ui.component.MeshtasticNavigationSuite
 import org.meshtastic.core.ui.viewmodel.UIViewModel
 import org.meshtastic.desktop.navigation.desktopNavGraph
 
 /**
- * Desktop main screen — Navigation 3 shell with adaptive navigation and shared [MeshtasticNavDisplay].
- *
- * 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.
+ * Desktop main screen — uses shared navigation components.
  */
 @Composable
-@Suppress("LongMethod")
-fun DesktopMainScreen(backStack: NavBackStack<NavKey>, uiViewModel: UIViewModel = koinViewModel()) {
-    Surface(modifier = Modifier.fillMaxSize(), color = MaterialTheme.colorScheme.background) {
+fun DesktopMainScreen(uiViewModel: UIViewModel) {
+    val backStack = androidx.navigation3.runtime.rememberNavBackStack(MeshtasticNavSavedStateConfig, NodesRoutes.NodesGraph as NavKey)
+
+    Surface(modifier = Modifier.fillMaxSize()) {
         MeshtasticAppShell(
             backStack = backStack,
             uiViewModel = uiViewModel,
             hostModifier = Modifier.padding(bottom = 24.dp),
         ) {
-            org.meshtastic.core.ui.component.MeshtasticNavigationSuite(
-                backStack = backStack,
-                uiViewModel = uiViewModel,
-            ) {
-                val provider = entryProvider<NavKey> { desktopNavGraph(backStack, uiViewModel) }
-
+            MeshtasticNavigationSuite(backStack = backStack, uiViewModel = uiViewModel, modifier = Modifier.fillMaxSize()) {
+                val provider = entryProvider<NavKey> {
+                    desktopNavGraph(backStack, uiViewModel)
+                }
                 MeshtasticNavDisplay(backStack = backStack, entryProvider = provider, modifier = Modifier.fillMaxSize())
             }
         }

feature/intro/src/androidMain/kotlin/org/meshtastic/feature/intro/AppIntroductionScreen.kt

@@ -24,6 +24,7 @@ import com.google.accompanist.permissions.ExperimentalPermissionsApi
 import com.google.accompanist.permissions.PermissionState
 import com.google.accompanist.permissions.rememberMultiplePermissionsState
 import com.google.accompanist.permissions.rememberPermissionState
+import org.meshtastic.core.ui.component.MeshtasticNavDisplay
 
 /**
  * Main application introduction screen. This Composable hosts the navigation flow and hoists the permission states.
@@ -56,7 +57,7 @@ fun AppIntroductionScreen(onDone: () -> Unit, viewModel: IntroViewModel) {
 
     val backStack = rememberNavBackStack(Welcome)
 
-    org.meshtastic.core.ui.component.MeshtasticNavDisplay(
+    MeshtasticNavDisplay(
         backStack = backStack,
         entryProvider =
         introNavGraph(