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/commonTest/kotlin/com/tt/honeyDue/storage/BiometricPreferenceTest.kt

@@ -0,0 +1,20 @@
+package com.tt.honeyDue.storage
+
+import kotlin.test.Test
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+/**
+ * Tests for BiometricPreference object.
+ * Tests the common wrapper logic (not platform-specific storage).
+ */
+class BiometricPreferenceTest {
+
+    @Test
+    fun biometricPreferenceDefaultsToFalseWhenNotInitialized() {
+        // When no manager is initialized, isBiometricEnabled should return false
+        val uninitializedPreference = BiometricPreference
+        // Note: This tests the fallback behavior when manager is null
+        assertFalse(uninitializedPreference.isBiometricEnabled())
+    }
+}