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.

iosApp/iosApp/Helpers/ErrorMessageParser.swift

@@ -28,6 +28,7 @@ enum ErrorMessageParser {
 
         // Password reset errors
         "error.rate_limit_exceeded": "Too many attempts. Please wait a few minutes and try again.",
+        "error.too_many_requests": "Too many requests. Please try again later.",
         "error.too_many_attempts": "Too many attempts. Please request a new code.",
         "error.invalid_reset_token": "This reset link has expired. Please request a new one.",
         "error.password_reset_failed": "Password reset failed. Please try again.",
@@ -148,7 +149,8 @@ enum ErrorMessageParser {
         ("ConnectException", "Unable to connect. Please check your internet connection."),
         ("SocketTimeoutException", "Request timed out. Please try again."),
         ("Connection refused", "Unable to connect. The server may be temporarily unavailable."),
-        ("Connection reset", "Connection lost. Please try again.")
+        ("Connection reset", "Connection lost. Please try again."),
+        ("Too many requests", "Too many requests. Please try again later.")
     ]
 
     // MARK: - Technical Error Indicators