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/storage/BiometricPreferenceManager.ios.kt

@@ -0,0 +1,28 @@
+package com.tt.honeyDue.storage
+
+import platform.Foundation.NSUserDefaults
+
+/**
+ * iOS implementation of biometric preference storage using NSUserDefaults.
+ * Follows the same pattern as ThemeStorageManager.ios.kt.
+ */
+actual class BiometricPreferenceManager {
+    private val defaults = NSUserDefaults.standardUserDefaults
+
+    actual fun isBiometricEnabled(): Boolean {
+        return defaults.boolForKey(KEY_BIOMETRIC_ENABLED)
+    }
+
+    actual fun setBiometricEnabled(enabled: Boolean) {
+        defaults.setBool(enabled, forKey = KEY_BIOMETRIC_ENABLED)
+        defaults.synchronize()
+    }
+
+    companion object {
+        private const val KEY_BIOMETRIC_ENABLED = "biometric_enabled"
+
+        private val instance by lazy { BiometricPreferenceManager() }
+
+        fun getInstance(): BiometricPreferenceManager = instance
+    }
+}