feat: add unit mapping functionality

- Added new API path for unit mappings in `api_paths.dart`.
- Implemented `upsertUnitMapping` method in `ImportRepository` to handle unit mapping creation.
- Updated `ReceiptImportTab` to learn and save unit mappings during receipt import.
- Created DTO for unit mapping with validation in `create-unit-mapping.dto.ts`.
- Added SQL migration for `UnitMapping` table creation with necessary constraints.

backend/dist/receipt-import/receipt-import.service.spec.js

@@ -32,6 +32,7 @@ describe('ReceiptImportService test matrix', () => {
         category: { findMany: jest.fn().mockResolvedValue([]) },
         receiptAlias: { findMany: jest.fn().mockResolvedValue([]) },
         product: { findMany: jest.fn().mockResolvedValue([]) },
+        unitMapping: { findMany: jest.fn().mockResolvedValue([]) },
     };
     const aiServiceMock = {
         suggestCategory: jest.fn(),
@@ -44,6 +45,7 @@ describe('ReceiptImportService test matrix', () => {
         jest.clearAllMocks();
         prismaMock.receiptAlias.findMany.mockResolvedValue([]);
         prismaMock.product.findMany.mockResolvedValue([]);
+        prismaMock.unitMapping.findMany.mockResolvedValue([]);
     });
     describe('ignore patterns', () => {
         it.each([
@@ -171,6 +173,31 @@ describe('ReceiptImportService test matrix', () => {
             expect(second[0].matchedProductName).toBe('Mjolk');
             expect(second[0].suggestedProductId).toBeUndefined();
         });
+        it('använder inlärd enhetsmappning vid aliasträff', async () => {
+            prismaMock.receiptAlias.findMany.mockResolvedValue([
+                {
+                    receiptName: 'mjolk 1l',
+                    productId: 501,
+                    product: {
+                        id: 501,
+                        name: 'Mjolk user',
+                        canonicalName: 'Mjolk user',
+                        categoryId: 30,
+                        categoryRef: { id: 30, name: 'Mejeri' },
+                    },
+                },
+            ]);
+            prismaMock.unitMapping.findMany.mockResolvedValue([
+                {
+                    productId: 501,
+                    originalUnit: 'l',
+                    preferredUnit: 'st',
+                },
+            ]);
+            const result = await service.matchProducts([{ rawName: 'MJOLK 1L', unit: 'L' }], 77);
+            expect(result[0].matchedProductId).toBe(501);
+            expect(result[0].unit).toBe('st');
+        });
     });
 });
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