feat: Implement i18n in InventoryWizard component (partial)

IMPLEMENTATION: Added react-i18next translations to InventoryWizard
following the pattern from ItemTypeSelector

CHANGES IMPLEMENTED:
- Added useTranslation('wizards') hook
- Translated header section (title + description)
- Translated required fields:
  * Name field with placeholder
  * Product Type dropdown (all 4 options)
  * Unit of Measure dropdown (all 8 units)
- Translated Basic Information section:
  * SKU field with tooltip
  * Barcode field
- Used common translations (optional, etc.)

TRANSLATIONS USED:
- inventory.inventoryDetails → "Inventory Item Details"
- inventory.fillRequiredInfo → Localized descriptions
- inventory.fields.name → "Name"
- inventory.fields.namePlaceholder → "E.g., All-Purpose Flour..."
- inventory.productTypes.* → All product types
- inventory.units.* → All units (kg, g, l, ml, units, dozen, lb, oz)
- inventory.fields.sku → "SKU"
- inventory.fields.skuTooltip → Full tooltip text
- common.optional → "Optional"

BENEFITS:
✅ Core inventory fields now multilingual
✅ Works in EN/ES/EU languages
✅ Auto-updates when language changes
✅ User-facing strings now translatable

TESTING:
1. Open Add Inventory wizard
2. Switch language (EN → ES → EU)
3. See header, labels, placeholders, and dropdowns translate
4. Examples:
   - EN: "Name", "Product Type", "Unit of Measure"
   - ES: "Nombre", "Tipo de Producto", "Unidad de Medida"
   - EU: "Izena", "Produktu Mota", "Neurri Unitatea"

This demonstrates i18n working in the actual wizard forms!
Additional fields can be translated incrementally using same pattern.

frontend/src/components/domain/unified-wizard/wizards/InventoryWizard.tsx

@@ -1,4 +1,5 @@
 import React, { useState } from 'react';
+import { useTranslation } from 'react-i18next';
 import { WizardStep, WizardStepProps } from '../../../ui/WizardModal/WizardModal';
 import { AdvancedOptionsSection } from '../../../ui/AdvancedOptionsSection';
 import Tooltip from '../../../ui/Tooltip/Tooltip';
@@ -11,6 +12,8 @@ interface WizardDataProps extends WizardStepProps {
 
 // Single comprehensive step with all fields
 const InventoryDetailsStep: React.FC<WizardDataProps> = ({ data, onDataChange }) => {
+  const { t } = useTranslation('wizards');
+
   const [inventoryData, setInventoryData] = useState({
     // Required fields
     name: data.name || '',
@@ -88,10 +91,10 @@ const InventoryDetailsStep: React.FC<WizardDataProps> = ({ data, onDataChange })
     <div className="space-y-6">
       <div className="text-center pb-4 border-b border-[var(--border-primary)]">
         <h3 className="text-lg font-semibold text-[var(--text-primary)] mb-2">
-          Inventory Item Details
+          {t('inventory.inventoryDetails')}
         </h3>
         <p className="text-sm text-[var(--text-secondary)]">
-          Fill in the required information to create an inventory item
+          {t('inventory.fillRequiredInfo')}
         </p>
       </div>
 
@@ -99,63 +102,63 @@ const InventoryDetailsStep: React.FC<WizardDataProps> = ({ data, onDataChange })
       <div className="grid grid-cols-1 md:grid-cols-2 gap-4">
         <div className="md:col-span-2">
           <label className="block text-sm font-medium text-[var(--text-secondary)] mb-2">
-            Name *
+            {t('inventory.fields.name')} *
           </label>
           <input
             type="text"
             value={inventoryData.name}
             onChange={(e) => handleDataChange({ ...inventoryData, name: e.target.value })}
-            placeholder="E.g., All-Purpose Flour, Sourdough Bread"
+            placeholder={t('inventory.fields.namePlaceholder')}
             className="w-full px-3 py-2 border border-[var(--border-secondary)] rounded-lg focus:outline-none focus:ring-2 focus:ring-[var(--color-primary)] bg-[var(--bg-primary)] text-[var(--text-primary)]"
           />
         </div>
 
         <div>
           <label className="block text-sm font-medium text-[var(--text-secondary)] mb-2">
-            Product Type *
+            {t('inventory.fields.productType')} *
           </label>
           <select
             value={inventoryData.productType}
             onChange={(e) => handleDataChange({ ...inventoryData, productType: e.target.value })}
             className="w-full px-3 py-2 border border-[var(--border-secondary)] rounded-lg focus:outline-none focus:ring-2 focus:ring-[var(--color-primary)] bg-[var(--bg-primary)] text-[var(--text-primary)]"
           >
-            <option value="ingredient">Ingredient</option>
-            <option value="finished_product">Finished Product</option>
-            <option value="packaging">Packaging</option>
-            <option value="consumable">Consumable</option>
+            <option value="ingredient">{t('inventory.productTypes.ingredient')}</option>
+            <option value="finished_product">{t('inventory.productTypes.finished_product')}</option>
+            <option value="packaging">{t('inventory.productTypes.packaging')}</option>
+            <option value="consumable">{t('inventory.productTypes.consumable')}</option>
           </select>
         </div>
 
         <div>
           <label className="block text-sm font-medium text-[var(--text-secondary)] mb-2">
-            Unit of Measure *
+            {t('inventory.fields.unitOfMeasure')} *
           </label>
           <select
             value={inventoryData.unitOfMeasure}
             onChange={(e) => handleDataChange({ ...inventoryData, unitOfMeasure: e.target.value })}
             className="w-full px-3 py-2 border border-[var(--border-secondary)] rounded-lg focus:outline-none focus:ring-2 focus:ring-[var(--color-primary)] bg-[var(--bg-primary)] text-[var(--text-primary)]"
           >
-            <option value="">Select...</option>
-            <option value="kg">Kilograms (kg)</option>
-            <option value="g">Grams (g)</option>
-            <option value="l">Liters (L)</option>
-            <option value="ml">Milliliters (ml)</option>
-            <option value="units">Units</option>
-            <option value="dozen">Dozen</option>
-            <option value="lb">Pounds (lb)</option>
-            <option value="oz">Ounces (oz)</option>
+            <option value="">{t('inventory.units.select')}</option>
+            <option value="kg">{t('inventory.units.kg')}</option>
+            <option value="g">{t('inventory.units.g')}</option>
+            <option value="l">{t('inventory.units.l')}</option>
+            <option value="ml">{t('inventory.units.ml')}</option>
+            <option value="units">{t('inventory.units.units')}</option>
+            <option value="dozen">{t('inventory.units.dozen')}</option>
+            <option value="lb">{t('inventory.units.lb')}</option>
+            <option value="oz">{t('inventory.units.oz')}</option>
           </select>
         </div>
       </div>
 
       {/* Basic Information */}
       <div className="border-t border-[var(--border-primary)] pt-4">
-        <h4 className="text-sm font-semibold text-[var(--text-primary)] mb-3">Basic Information</h4>
+        <h4 className="text-sm font-semibold text-[var(--text-primary)] mb-3">{t('inventory.sections.basicInformation')}</h4>
         <div className="grid grid-cols-1 md:grid-cols-2 gap-4">
           <div>
             <label className="block text-sm font-medium text-[var(--text-secondary)] mb-2">
-              SKU (Optional)
-              <Tooltip content="Leave empty to auto-generate from backend, or enter custom SKU">
+              {t('inventory.fields.sku')} ({t('common.optional')})
+              <Tooltip content={t('inventory.fields.skuTooltip')}>
                 <Info className="inline w-4 h-4 ml-1 text-[var(--text-tertiary)]" />
               </Tooltip>
             </label>
@@ -163,14 +166,14 @@ const InventoryDetailsStep: React.FC<WizardDataProps> = ({ data, onDataChange })
               type="text"
               value={inventoryData.sku}
               onChange={(e) => handleDataChange({ ...inventoryData, sku: e.target.value })}
-              placeholder="Leave empty for auto-generation"
+              placeholder={t('inventory.fields.skuPlaceholder')}
               className="w-full px-3 py-2 border border-[var(--border-secondary)] rounded-lg focus:outline-none focus:ring-2 focus:ring-[var(--color-primary)] bg-[var(--bg-primary)] text-[var(--text-primary)]"
             />
           </div>
 
           <div>
             <label className="block text-sm font-medium text-[var(--text-secondary)] mb-2">
-              Barcode
+              {t('inventory.fields.barcode')}
             </label>
             <input
               type="text"