Fix invalid unit_of_measure 'dozen' causing 422 API errors

**Issue:**
Creating ingredients failed with 422 error:
```
Input should be 'kg', 'g', 'l', 'ml', 'units', 'pcs', 'pkg', 'bags' or 'boxes'
input: "dozen"
```

**Root Cause:**
Frontend was using units not supported by backend UnitOfMeasure enum:
- "dozen" (docena)
- "cup" (taza)
- "tbsp" (cucharada)
- "tsp" (cucharadita)
- "piece" → should be "pcs"
- "package" → should be "pkg"
- "bag" → should be "bags"
- "box" → should be "boxes"

**Backend Supported Units (inventory.ts:28-38):**
kg, g, l, ml, units, pcs, pkg, bags, boxes

**Solution:**
Replaced all invalid units with backend-compatible ones across codebase.

**Files Modified:**

1. **UploadSalesDataStep.tsx:604**
   - Before: ['kg', 'g', 'L', 'ml', 'units', 'dozen']
   - After: ['kg', 'g', 'l', 'ml', 'units', 'pcs', 'pkg', 'bags', 'boxes']

2. **BatchAddIngredientsModal.tsx:53**
   - Before: ['kg', 'g', 'L', 'ml', 'units', 'dozen']
   - After: ['kg', 'g', 'l', 'ml', 'units', 'pcs', 'pkg', 'bags', 'boxes']

3. **QuickAddIngredientModal.tsx:69**
   - Before: ['kg', 'g', 'L', 'ml', 'units', 'dozen']
   - After: ['kg', 'g', 'l', 'ml', 'units', 'pcs', 'pkg', 'bags', 'boxes']

4. **inventory/index.ts:51-62**
   - Removed: 'piece', 'package', 'bag', 'box', 'dozen', 'cup', 'tbsp', 'tsp'
   - Added: 'units', 'pcs', 'pkg', 'bags', 'boxes'
   - Added comment: "must match backend UnitOfMeasure enum exactly"

5. **ingredientHelpers.ts:168**
   - Eggs unit changed from 'dozen' → 'units'

6. **utils/constants.ts:77-87**
   - Removed volume units: cup, tbsp, tsp
   - Removed count units: piece, dozen, package, bag, box
   - Added: units, pcs, pkg, bags, boxes
   - Now matches backend enum exactly

**Also Fixed:**
- Changed 'L' to lowercase 'l' for consistency with backend

**Impact:**
✅ All ingredient creation now uses valid backend units
✅ No more 422 validation errors
✅ Frontend/backend unit enums synchronized

**Build Status:** ✓ Successful in 22.23s

frontend/src/components/domain/inventory/BatchAddIngredientsModal.tsx

@@ -50,7 +50,7 @@ export const BatchAddIngredientsModal: React.FC<BatchAddIngredientsModalProps> =
     'Other'
   ];
 
-  const unitOptions = ['kg', 'g', 'L', 'ml', 'units', 'dozen'];
+  const unitOptions = ['kg', 'g', 'l', 'ml', 'units', 'pcs', 'pkg', 'bags', 'boxes'];
 
   const updateRow = (id: string, field: keyof BatchIngredientRow, value: any) => {
     setRows(rows.map(row =>

frontend/src/components/domain/inventory/QuickAddIngredientModal.tsx

@@ -66,7 +66,7 @@ export const QuickAddIngredientModal: React.FC<QuickAddIngredientModalProps> = (
     'Other'
   ];
 
-  const unitOptions = ['kg', 'g', 'L', 'ml', 'units', 'dozen'];
+  const unitOptions = ['kg', 'g', 'l', 'ml', 'units', 'pcs', 'pkg', 'bags', 'boxes'];
 
   // Check for duplicates when name changes
   useEffect(() => {

frontend/src/components/domain/inventory/index.ts

@@ -48,20 +48,17 @@ export const INVENTORY_CONSTANTS = {
     { value: 'out', label: 'Sin Stock' },
   ],
 
-  // Units of measure commonly used in Spanish bakeries
+  // Units of measure - must match backend UnitOfMeasure enum exactly
   BAKERY_UNITS: [
     { value: 'kg', label: 'Kilogramo (kg)' },
     { value: 'g', label: 'Gramo (g)' },
     { value: 'l', label: 'Litro (l)' },
     { value: 'ml', label: 'Mililitro (ml)' },
-    { value: 'piece', label: 'Pieza (pz)' },
+    { value: 'units', label: 'Unidades' },
-    { value: 'package', label: 'Paquete' },
+    { value: 'pcs', label: 'Piezas' },
-    { value: 'bag', label: 'Bolsa' },
+    { value: 'pkg', label: 'Paquetes' },
-    { value: 'box', label: 'Caja' },
+    { value: 'bags', label: 'Bolsas' },
-    { value: 'dozen', label: 'Docena' },
+    { value: 'boxes', label: 'Cajas' },
-    { value: 'cup', label: 'Taza' },
-    { value: 'tbsp', label: 'Cucharada' },
-    { value: 'tsp', label: 'Cucharadita' },
   ],
 
   // Default form values for new ingredients

frontend/src/components/domain/inventory/ingredientHelpers.ts

@@ -165,7 +165,7 @@ export const commonIngredientTemplates: IngredientTemplate[] = [
   {
     name: 'Huevos',
     category: 'Dairy',
-    unit_of_measure: 'dozen',
+    unit_of_measure: 'units',
     icon: '🥚',
     estimated_shelf_life_days: 21,
     requires_refrigeration: true,

frontend/src/components/domain/onboarding/steps/UploadSalesDataStep.tsx

@@ -601,7 +601,7 @@ export const UploadSalesDataStep: React.FC<UploadSalesDataStepProps> = ({
     'Other'
   ];
 
-  const unitOptions = ['kg', 'g', 'L', 'ml', 'units', 'dozen'];
+  const unitOptions = ['kg', 'g', 'l', 'ml', 'units', 'pcs', 'pkg', 'bags', 'boxes'];
 
   // INVENTORY LIST VIEW (after AI suggestions loaded)
   if (showInventoryStep) {

frontend/src/utils/constants.ts

@@ -77,16 +77,13 @@ export const UNITS_OF_MEASURE = {
   volume: {
     l: { label: 'Litro', symbol: 'l', factor: 1000 },
     ml: { label: 'Mililitro', symbol: 'ml', factor: 1 },
-    cup: { label: 'Taza', symbol: 'taza', factor: 240 },
-    tbsp: { label: 'Cucharada', symbol: 'cda', factor: 15 },
-    tsp: { label: 'Cucharadita', symbol: 'cdta', factor: 5 },
   },
   count: {
-    piece: { label: 'Pieza', symbol: 'pz', factor: 1 },
+    units: { label: 'Unidades', symbol: 'ud', factor: 1 },
-    dozen: { label: 'Docena', symbol: 'doc', factor: 12 },
+    pcs: { label: 'Piezas', symbol: 'pz', factor: 1 },
-    package: { label: 'Paquete', symbol: 'paq', factor: 1 },
+    pkg: { label: 'Paquetes', symbol: 'paq', factor: 1 },
-    bag: { label: 'Bolsa', symbol: 'bolsa', factor: 1 },
+    bags: { label: 'Bolsas', symbol: 'bolsa', factor: 1 },
-    box: { label: 'Caja', symbol: 'caja', factor: 1 },
+    boxes: { label: 'Cajas', symbol: 'caja', factor: 1 },
   },
 } as const;