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 =>