Fix UI interpolation and add i18n translations to onboarding steps

Fix multiple onboarding UI issues:

1. **ReviewSetupStep interpolation fix:**
   - Change single braces {suppliers} to double braces {{suppliers}}
   - Fix {ingredients} and {recipes} interpolation to {{ingredients}}, {{recipes}}
   - This resolves the issue where raw placeholders were displayed instead of actual values

2. **CompletionStep i18n translations:**
   - Add useTranslation hook import
   - Replace all hardcoded Spanish text with translation keys
   - Add translation support for: welcome message, bakery info, inventory,
     AI training, setup guide, next steps sections, and help text
   - Properly interpolate bakery name using {{name}} syntax
   - Ensures widget works in all 3 supported languages (ES, EN, PT)

3. **Confirmed onboarding steps presence:**
   - suppliers-setup step exists (conditional on stockEntryCompleted)
   - ml-training step exists (conditional on aiAnalysisComplete)
   - Both steps are properly configured in UnifiedOnboardingWizard

These changes ensure proper variable interpolation in i18next and
complete internationalization support for the onboarding completion flow.

frontend/src/components/domain/setup-wizard/steps/ReviewSetupStep.tsx

@@ -289,7 +289,7 @@ export const ReviewSetupStep: React.FC<SetupStepProps> = ({ onUpdate, onComplete
             </h3>
             <p className="text-[var(--text-secondary)] max-w-xl mx-auto">
               {t('setup_wizard:review.ready_message',
-                "You've successfully configured {suppliers} suppliers, {ingredients} ingredients, and {recipes} recipes. Click 'Complete Setup' to finish and start using the system.",
+                "You've successfully configured {{suppliers}} suppliers, {{ingredients}} ingredients, and {{recipes}} recipes. Click 'Complete Setup' to finish and start using the system.",
                 { suppliers: suppliers.length, ingredients: ingredients.length, recipes: recipes.length }
               )}
             </p>