Harden auth, payments, and frontend against review findings.

Close exploitable gaps in booking/payment flows, enforce token versioning and account checks, gate sensitive payment data, and add middleware plus input validation across admin routes.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/components/GoogleSignInButton.tsx

@@ -3,6 +3,7 @@
 import { useEffect, useRef, useState, useCallback } from 'react';
 import { useAuth } from '@/context/AuthContext';
 import { useLanguage } from '@/context/LanguageContext';
+import { safeInternalPath } from '@/lib/safeRedirect';
 import toast from 'react-hot-toast';
 
 declare global {
@@ -82,10 +83,9 @@ export default function GoogleSignInButton({
         toast.success(locale === 'es' ? 'Bienvenido!' : 'Welcome!');
         onSuccess?.();
         
-        // Use window.location for navigation to ensure clean state
-        if (redirectTo) {
-          window.location.href = redirectTo;
-        }
+        // Use window.location for navigation to ensure clean state.
+        // Constrain to a same-origin path to avoid open redirects.
+        window.location.href = safeInternalPath(redirectTo, '/dashboard');
       } catch (error: unknown) {
         const errorMessage = error instanceof Error ? error.message : 'Google login failed';
         const displayError = locale === 'es' ? 'Error al iniciar sesion con Google' : errorMessage;