fix: use offset+clipToBounds instead of graphicsLayer alpha for tab keep-alive

Hidden tabs with graphicsLayer{alpha=0f} still intercepted touch events.
Replaced with offset(x=2000.dp) + parent clipToBounds() so hidden composables
are off-screen and cannot capture touches meant for the visible tab.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/src/main/java/top/yeij/cyrene/ui/navigation/NavGraph.kt

@@ -5,6 +5,7 @@ import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.fillMaxHeight
 import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.offset
 import androidx.compose.foundation.layout.statusBarsPadding
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.automirrored.filled.Chat
@@ -21,7 +22,8 @@ import androidx.compose.runtime.mutableIntStateOf
 import androidx.compose.runtime.saveable.rememberSaveable
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.graphics.graphicsLayer
+import androidx.compose.ui.draw.clipToBounds
+import androidx.compose.ui.unit.dp
 import androidx.navigation.NavHostController
 import androidx.navigation.compose.NavHost
 import androidx.navigation.compose.composable
@@ -145,28 +147,29 @@ fun MainScreen(
             modifier = Modifier
                 .weight(1f)
                 .fillMaxHeight()
+                .clipToBounds()
                 .background(MaterialTheme.colorScheme.background),
         ) {
-            // Keep all tabs composed to avoid destroying ChatScreen on tab switch.
-            // Hidden tabs use graphicsLayer { alpha = 0f } — invisible but alive.
+            // Keep all tabs alive by offsetting hidden ones off-screen.
+            // clipToBounds ensures they don't intercept touches outside the visible area.
             Box(
                 modifier = Modifier
                     .fillMaxSize()
-                    .graphicsLayer { alpha = if (selectedTab == 0) 1f else 0f },
+                    .offset(x = if (selectedTab == 0) 0.dp else 2000.dp),
             ) {
                 ChatScreen()
             }
             Box(
                 modifier = Modifier
                     .fillMaxSize()
-                    .graphicsLayer { alpha = if (selectedTab == 1) 1f else 0f },
+                    .offset(x = if (selectedTab == 1) 0.dp else 2000.dp),
             ) {
                 IoTScreen()
             }
             Box(
                 modifier = Modifier
                     .fillMaxSize()
-                    .graphicsLayer { alpha = if (selectedTab == 2) 1f else 0f },
+                    .offset(x = if (selectedTab == 2) 0.dp else 2000.dp),
             ) {
                 ProfileScreen(
                     onNavigateToSettings = { navController.navigate(Routes.SETTINGS) },