fix(app): persist active tab state and support bottom sheet scrolling

- Use rememberSaveable for activeTab in MainAppShell to survive configuration changes and process death
- Add vertical scrolling to AccountProviderBottomSheet to prevent overflow on small screens and landscape orientation
- Clean up unused imports and update KDoc in AccountProviderBottomSheet

android/app/src/main/kotlin/com/flagship/abox/manager/ui/shell/AccountProviderBottomSheet.kt

@@ -10,12 +10,13 @@ import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.foundation.verticalScroll
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.automirrored.filled.ExitToApp
 import androidx.compose.material.icons.filled.CloudDone
-import androidx.compose.material3.ButtonDefaults
 import androidx.compose.material3.Card
 import androidx.compose.material3.CardDefaults
 import androidx.compose.material3.ExperimentalMaterial3Api
@@ -23,7 +24,6 @@ import androidx.compose.material3.HorizontalDivider
 import androidx.compose.material3.Icon
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.ModalBottomSheet
-import androidx.compose.material3.OutlinedButton
 import androidx.compose.material3.SheetState
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
@@ -41,7 +41,7 @@ import com.flagship.abox.manager.designsystem.ABoxUserAvatar
 
 /**
  * Account and Provider management bottom sheet triggered by clicking the top bar user avatar.
- * Allows viewing current session info, switching providers, and signing out.
+ * Allows viewing current session info and signing out.
  */
 @OptIn(ExperimentalMaterial3Api::class)
 @Composable
@@ -64,6 +64,7 @@ fun AccountProviderBottomSheet(
         Column(
             modifier = Modifier
                 .fillMaxWidth()
+                .verticalScroll(rememberScrollState())
                 .padding(horizontal = 24.dp)
                 .padding(bottom = 32.dp),
             horizontalAlignment = Alignment.CenterHorizontally,

android/app/src/main/kotlin/com/flagship/abox/manager/ui/shell/MainAppShell.kt

@@ -18,6 +18,7 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.runtime.saveable.rememberSaveable
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
@@ -53,7 +54,7 @@ fun MainAppShell(
     scenesSlot: @Composable () -> Unit = { DefaultScenesSlot() },
     activitySlot: @Composable () -> Unit = { DefaultActivitySlot() },
 ) {
-    var activeTab by remember(initialTab) { mutableStateOf(initialTab) }
+    var activeTab by rememberSaveable { mutableStateOf(initialTab) }
     var showAccountSheet by remember { mutableStateOf(false) }
 
     Scaffold(