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/jvmMain/kotlin/com/tt/honeyDue/platform/BiometricAuth.jvm.kt

@@ -0,0 +1,24 @@
+package com.tt.honeyDue.platform
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
+
+/**
+ * JVM/Desktop implementation - biometric auth not available on desktop.
+ */
+class JvmBiometricAuthPerformer : BiometricAuthPerformer {
+    override fun isBiometricAvailable(): Boolean = false
+
+    override fun authenticate(
+        title: String,
+        subtitle: String,
+        onResult: (BiometricResult) -> Unit
+    ) {
+        onResult(BiometricResult.NotAvailable)
+    }
+}
+
+@Composable
+actual fun rememberBiometricAuth(): BiometricAuthPerformer {
+    return remember { JvmBiometricAuthPerformer() }
+}