Add biometric lock and rate limit handling

Biometric lock: opt-in Face ID/Touch ID/fingerprint app lock with toggle
in ProfileScreen. Locks on background, requires auth on foreground return.
Platform implementations: BiometricPrompt (Android), LAContext (iOS).

Rate limit: 429 responses parsed with Retry-After header, user-friendly
error messages in all 10 locales, retry plugin respects 429.
ErrorMessageParser updated for both iOS Swift and KMM.

composeApp/src/commonMain/kotlin/com/tt/honeyDue/App.kt

@@ -60,6 +60,12 @@ import com.tt.honeyDue.network.APILayer
 import com.tt.honeyDue.platform.ContractorImportHandler
 import com.tt.honeyDue.platform.PlatformUpgradeScreen
 import com.tt.honeyDue.platform.ResidenceImportHandler
+import com.tt.honeyDue.storage.BiometricPreference
+import com.tt.honeyDue.ui.screens.BiometricLockScreen
+import androidx.compose.runtime.saveable.rememberSaveable
+import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.LifecycleEventObserver
+import androidx.lifecycle.compose.LocalLifecycleOwner
 
 import honeydue.composeapp.generated.resources.Res
 import honeydue.composeapp.generated.resources.compose_multiplatform
@@ -82,6 +88,28 @@ fun App(
     var hasCompletedOnboarding by remember { mutableStateOf(DataManager.hasCompletedOnboarding.value) }
     val navController = rememberNavController()
 
+    // Biometric lock state - starts locked if biometric is enabled and user is logged in
+    var isLocked by rememberSaveable {
+        mutableStateOf(BiometricPreference.isBiometricEnabled() && DataManager.authToken.value != null)
+    }
+
+    // Lock the app when returning from background
+    val lifecycleOwner = LocalLifecycleOwner.current
+    DisposableEffect(lifecycleOwner) {
+        val observer = LifecycleEventObserver { _, event ->
+            if (event == Lifecycle.Event.ON_STOP) {
+                // App going to background - lock if biometric is enabled
+                if (BiometricPreference.isBiometricEnabled() && DataManager.authToken.value != null) {
+                    isLocked = true
+                }
+            }
+        }
+        lifecycleOwner.lifecycle.addObserver(observer)
+        onDispose {
+            lifecycleOwner.lifecycle.removeObserver(observer)
+        }
+    }
+
     // Handle navigation from notification tap
     // Note: The actual navigation to the task column happens in MainScreen -> AllTasksScreen
     // We just need to ensure the user is on MainRoute when a task navigation is requested
@@ -156,6 +184,7 @@ fun App(
             else -> MainRoute
         }
 
+        Box(modifier = Modifier.fillMaxSize()) {
         Surface(
             modifier = Modifier.fillMaxSize(),
             color = MaterialTheme.colorScheme.background
@@ -692,6 +721,14 @@ fun App(
             }
         }
         }
+
+        // Biometric lock overlay - shown when app is locked
+        if (isLocked && isLoggedIn && isVerified) {
+            BiometricLockScreen(
+                onUnlocked = { isLocked = false }
+            )
+        }
+        } // close Box
     }