feat: Add backward navigation and comprehensive i18n support

- Implement backward navigation in onboarding wizard with state persistence
- Add comprehensive setup wizard translations (Spanish, English, Basque)
- Add configuration widget translations for dashboard
- Support for Suppliers, Recipes, Quality, and Team setup steps

New translation files:
- setup_wizard.json for all 3 languages (es, en, eu)
- Added config section to dashboard.json files

Key improvements:
- Users can now navigate backwards through wizard steps
- All setup wizard steps now have proper i18n support
- Configuration progress widget fully translated

frontend/src/components/domain/onboarding/UnifiedOnboardingWizard.tsx

@@ -409,6 +409,16 @@ const OnboardingWizardContent: React.FC = () => {
     }
   };
 
+  const handleGoToPrevious = () => {
+    if (currentStepIndex > 0) {
+      const previousStep = VISIBLE_STEPS[currentStepIndex - 1];
+      console.log(`⬅️  Going back from "${currentStep.id}" to "${previousStep.id}"`);
+      setCurrentStepIndex(currentStepIndex - 1);
+    } else {
+      console.warn('⚠️  Already at first step, cannot go back');
+    }
+  };
+
   // Show loading state
   if (!isNewTenant && (isLoadingProgress || !isInitialized)) {
     return (
@@ -518,7 +528,7 @@ const OnboardingWizardContent: React.FC = () => {
         <CardBody padding="md">
           <StepComponent
             onNext={() => {}}
-            onPrevious={() => {}}
+            onPrevious={handleGoToPrevious}
             onComplete={handleStepComplete}
             onUpdate={handleStepUpdate}
             isFirstStep={currentStepIndex === 0}