feat(flyer-import): add cheese variant splitting and normalization rules

- Add logic to split Swedish cheese variants (Präst, Herrgård, Grevé) into separate products
- Implement brand normalization for "Arla Ko" and category assignment to "Hårdost"
- Update flyer parser with detailed rules for bundle/group announcements
- Add unit tests for variant splitting and brand/category normalization
- Replace single-item return with flatMap for expanded product lists

backend/src/flyer-import/services/flyer-normalizer.service.spec.ts

@@ -105,5 +105,41 @@ describe('FlyerNormalizerService', () => {
       const result2 = service.normalize(undefined as any);
       expect(result2).toEqual([]);
     });
+
+    it('splits listed cheese variants into separate products', () => {
+      const items = [
+        {
+          rawName: 'PRÄST®, HERRGÅRD®, GREVÉ®',
+          brand: 'ARLA KO',
+          unit: 'kg',
+          comparisonPrice: '79,90',
+          offer: ['Max 3 förp/hushåll'],
+        },
+      ];
+
+      const result = service.normalize(items);
+
+      expect(result).toHaveLength(3);
+      expect(result.map((item) => item.rawName)).toEqual(['Prastost', 'Herrgardsost', 'Greveost']);
+      expect(result.every((item) => item.brand === 'Arla Ko')).toBe(true);
+      expect(result.every((item) => item.categoryHint === 'Hårdost')).toBe(true);
+      expect(result[0].parseReasons).toContain('split_cheese_variants');
+    });
+
+    it('keeps single cheese item unsplit but normalizes brand/category', () => {
+      const items = [
+        {
+          rawName: 'Prästost',
+          brand: 'arla ko',
+        },
+      ];
+
+      const result = service.normalize(items);
+
+      expect(result).toHaveLength(1);
+      expect(result[0].rawName).toBe('Prästost');
+      expect(result[0].brand).toBe('Arla Ko');
+      expect(result[0].categoryHint).toBe('Hårdost');
+    });
   });
 });