Add email notification preference for task completion

- Add emailTaskCompleted field to NotificationPreference model
- Add email preference toggle to notification settings UI (iOS & Android)
- Add localized strings for email notifications section
- Update ViewModel to support email preference updates

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

composeApp/src/commonMain/kotlin/com/example/casera/ui/screens/NotificationPreferencesScreen.kt

@@ -35,6 +35,7 @@ fun NotificationPreferencesScreen(
     var taskAssigned by remember { mutableStateOf(true) }
     var residenceShared by remember { mutableStateOf(true) }
     var warrantyExpiring by remember { mutableStateOf(true) }
+    var emailTaskCompleted by remember { mutableStateOf(true) }
 
     // Load preferences on first render
     LaunchedEffect(Unit) {
@@ -51,6 +52,7 @@ fun NotificationPreferencesScreen(
             taskAssigned = prefs.taskAssigned
             residenceShared = prefs.residenceShared
             warrantyExpiring = prefs.warrantyExpiring
+            emailTaskCompleted = prefs.emailTaskCompleted
         }
     }
 
@@ -294,6 +296,36 @@ fun NotificationPreferencesScreen(
                         }
                     }
 
+                    // Email Notifications Section
+                    Text(
+                        stringResource(Res.string.notifications_email_section),
+                        style = MaterialTheme.typography.titleMedium,
+                        fontWeight = FontWeight.SemiBold,
+                        modifier = Modifier.padding(top = AppSpacing.md)
+                    )
+
+                    Card(
+                        modifier = Modifier.fillMaxWidth(),
+                        shape = RoundedCornerShape(AppRadius.md),
+                        colors = CardDefaults.cardColors(
+                            containerColor = MaterialTheme.colorScheme.surfaceVariant
+                        )
+                    ) {
+                        Column {
+                            NotificationToggle(
+                                title = stringResource(Res.string.notifications_email_task_completed),
+                                description = stringResource(Res.string.notifications_email_task_completed_desc),
+                                icon = Icons.Default.Email,
+                                iconTint = MaterialTheme.colorScheme.primary,
+                                checked = emailTaskCompleted,
+                                onCheckedChange = {
+                                    emailTaskCompleted = it
+                                    viewModel.updatePreference(emailTaskCompleted = it)
+                                }
+                            )
+                        }
+                    }
+
                     Spacer(modifier = Modifier.height(AppSpacing.xl))
                 }
             }