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/iosMain/kotlin/com/tt/honeyDue/platform/BiometricAuth.ios.kt

@@ -0,0 +1,57 @@
+package com.tt.honeyDue.platform
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
+import kotlinx.cinterop.ExperimentalForeignApi
+import platform.LocalAuthentication.LAContext
+import platform.LocalAuthentication.LAPolicyDeviceOwnerAuthenticationWithBiometrics
+import kotlinx.coroutines.MainScope
+import kotlinx.coroutines.launch
+
+/**
+ * iOS implementation of biometric authentication using LocalAuthentication framework (LAContext).
+ */
+@OptIn(ExperimentalForeignApi::class)
+class IOSBiometricAuthPerformer : BiometricAuthPerformer {
+
+    override fun isBiometricAvailable(): Boolean {
+        val context = LAContext()
+        return context.canEvaluatePolicy(
+            LAPolicyDeviceOwnerAuthenticationWithBiometrics,
+            error = null
+        )
+    }
+
+    override fun authenticate(
+        title: String,
+        subtitle: String,
+        onResult: (BiometricResult) -> Unit
+    ) {
+        if (!isBiometricAvailable()) {
+            onResult(BiometricResult.NotAvailable)
+            return
+        }
+
+        val context = LAContext()
+        context.localizedFallbackTitle = ""
+
+        context.evaluatePolicy(
+            LAPolicyDeviceOwnerAuthenticationWithBiometrics,
+            localizedReason = subtitle
+        ) { success, error ->
+            MainScope().launch {
+                if (success) {
+                    onResult(BiometricResult.Success)
+                } else {
+                    val message = error?.localizedDescription ?: "Authentication failed"
+                    onResult(BiometricResult.Failed(message))
+                }
+            }
+        }
+    }
+}
+
+@Composable
+actual fun rememberBiometricAuth(): BiometricAuthPerformer {
+    return remember { IOSBiometricAuthPerformer() }
+}