fix: apply elevation color thresholds on radar page

LocalElevationThresholds was provided inside MainScreen, but RadarDestination
is a root-level sibling entry in NavRoot's NavDisplay, so the radar page's
top bar fell outside the CompositionLocal scope and always used the default
15/45 thresholds instead of the user-configured ones.

Hoist the CompositionLocalProvider to NavRoot so both the tab content and
the root-level RadarDestination read the user's low/high elevation
thresholds, and drop the now-redundant provider from MainScreen.

app/src/main/java/com/rtbishop/look4sat/MainScreen.kt

@@ -99,6 +99,19 @@ fun NavRoot(deeplink: String? = null) {
     // Reverse: outgoing slides out to the right, incoming drifts in from the left
     val popTransition = slideInHorizontally(tween(300)) { -it / 3 } togetherWith
         slideOutHorizontally(tween(300)) { it }
+    // Elevation color thresholds must be provided at the root level so that BOTH
+    // the tab content (MainScreen) and the root-level RadarDestination see the
+    // user's custom thresholds. RadarDestination is a sibling entry of MainScreen
+    // in this NavDisplay, so a provider inside MainScreen never reaches it.
+    val context = LocalContext.current
+    val container = (context.applicationContext as IContainerProvider).getMainContainer()
+    val otherSettings by container.settingsRepo.otherSettings.collectAsStateWithLifecycle()
+    CompositionLocalProvider(
+        LocalElevationThresholds provides ElevationThresholds(
+            low = otherSettings.lowElevation,
+            high = otherSettings.highElevation
+        )
+    ) {
         NavDisplay(
             modifier = Modifier.fillMaxSize(),
             backStack = rootBackStack,
@@ -123,13 +136,13 @@ fun NavRoot(deeplink: String? = null) {
             }
         )
     }
+}
 
 @Composable
 private fun MainScreen(navigateToRadar: () -> Unit = {}) {
     val context = LocalContext.current
     val container = (context.applicationContext as IContainerProvider).getMainContainer()
     val trackingState by container.radioTrackingService.state.collectAsStateWithLifecycle()
-    val otherSettings by container.settingsRepo.otherSettings.collectAsStateWithLifecycle()
 
     val backStack = rememberNavBackStack(Screen.Passes)
     val currentKey = backStack.lastOrNull()
@@ -139,12 +152,6 @@ private fun MainScreen(navigateToRadar: () -> Unit = {}) {
     val navItems =
         listOf(Screen.Satellites, Screen.Passes, Screen.Status, Screen.Map, Screen.Settings)
 
-    CompositionLocalProvider(
-        LocalElevationThresholds provides ElevationThresholds(
-            low = otherSettings.lowElevation,
-            high = otherSettings.highElevation
-        )
-    ) {
     NavigationSuiteScaffold(
         navigationSuiteItems = {
             navItems.forEach { screen ->
@@ -224,7 +231,6 @@ private fun MainScreen(navigateToRadar: () -> Unit = {}) {
         }
     }
 }
-}
 
 @Composable
 private fun TrackingBanner(state: RadioTrackingState, onClick: () -> Unit) {