feat(ui): top-right 日程按钮 — add current/next pass to system calendar on radar and passes pages

Restores the original repo's calendar function (ic_calendar → AddToCalendar via
CalendarContract ACTION_INSERT) to the top-right of both pages, replacing the
map buttons:
- Radar page: back to upstream's addToCalendar (current pass name/aos/los).
- Passes page: new PassesAction.AddToCalendar wired through PassesViewModel +
  container.provideAddToCalendar() (next pass name/aos/los); left button back
  to the pass filter (reverts the earlier radios-button swap).
The map button is gone from both top bars — the map is now a bottom-nav tab.
Also drops the now-dead openMapRequest/navigateToMap navigation chain in
NavRoot/MainScreen that only the radar map button used.

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

@@ -51,7 +51,6 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.CompositionLocalProvider
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
-import androidx.compose.runtime.mutableIntStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
@@ -94,16 +93,11 @@ import com.rtbishop.look4sat.feature.status.SatStatusDestination
 fun NavRoot(deeplink: String? = null) {
     val rootBackStack = rememberNavBackStack(Screen.Passes)
     val deeplinkResolver = DeeplinkResolver()
-    var openMapRequest by remember { mutableIntStateOf(0) }
     LaunchedEffect(deeplink) {
         deeplink?.let { rootBackStack.add(deeplinkResolver.resolve(it)) }
     }
     val navigateBack: () -> Unit = { rootBackStack.removeLastOrNull() }
     val navigateToRadar: () -> Unit = { rootBackStack.add(RadarDestination) }
-    val navigateToMap: () -> Unit = {
-        while (rootBackStack.size > 1) rootBackStack.removeAt(rootBackStack.size - 1)
-        openMapRequest += 1
-    }
     // Incoming screen slides in from the right, outgoing drifts left at 1/3 speed (API35+ style)
     val pushTransition = slideInHorizontally(tween(300)) { it } togetherWith
         slideOutHorizontally(tween(300)) { -it / 3 }
@@ -124,9 +118,7 @@ fun NavRoot(deeplink: String? = null) {
         entryProvider = entryProvider {
             entry<Screen.Passes> {
                 MainScreen(
-                    navigateToRadar = navigateToRadar,
-                    openMapRequest = openMapRequest,
-                    onOpenMapRequestHandled = { openMapRequest = 0 }
+                    navigateToRadar = navigateToRadar
                 )
             }
             entry<RadarDestination> {
@@ -134,7 +126,7 @@ fun NavRoot(deeplink: String? = null) {
                     modifier = Modifier.fillMaxSize(),
                     color = MaterialTheme.colorScheme.background
                 ) {
-                    RadarDestination(navigateUp = navigateBack, navigateToMap = navigateToMap)
+                    RadarDestination(navigateUp = navigateBack)
                 }
             }
         }
@@ -143,23 +135,11 @@ fun NavRoot(deeplink: String? = null) {
 
 @Composable
 fun MainScreen(
-    navigateToRadar: () -> Unit = {},
-    openMapRequest: Int = 0,
-    onOpenMapRequestHandled: () -> Unit = {}
+    navigateToRadar: () -> Unit = {}
 ) {
     val backStack = rememberNavBackStack(Screen.Passes)
     val currentKey = backStack.lastOrNull()
     val navigateBack: () -> Unit = { backStack.removeLastOrNull() }
-    val navigateToMap: () -> Unit = {
-        while (backStack.size > 1) backStack.removeAt(backStack.size - 1)
-        backStack.add(Screen.Map)
-    }
-    LaunchedEffect(openMapRequest) {
-        if (openMapRequest > 0) {
-            navigateToMap()
-            onOpenMapRequestHandled()
-        }
-    }
     val fadeTransition = fadeIn(animationSpec = tween(350)) togetherWith fadeOut(animationSpec = tween(350))
     // Map sits at position 4 from the left, matching the upstream nav order
     // (Satellites, Passes, AMSAT/Status, Map, ...), with the fork's Mutual tab