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
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