fix(statistics): feeding totals per unit instead of adding litres to kilograms

The feeding statistics summed every amount regardless of its unit, so
5 l syrup and 2 kg fondant showed as 7. The API now also returns byUnit
(units normalised: "L" = "l"), the old fields stay for compatibility,
and the statistics page shows one list per unit.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

ApiCore-Backend/src/statistics/statistics.service.spec.ts

@@ -212,5 +212,25 @@ describe('StatisticsService', () => {
       expect(result.byColony).toEqual({ c1: 8, c2: 2 });
       expect(result.bySeason).toEqual({ '2025': 8, '2024': 2 });
     });
+
+    it('never adds litres and kilograms together', async () => {
+      prisma.feeding.findMany.mockResolvedValueOnce([
+        { colonyId: 'c1', date: new Date('2025-09-01'), amount: 5, unit: 'l' },
+        { colonyId: 'c1', date: new Date('2025-09-15'), amount: 2, unit: 'kg' },
+        {
+          colonyId: 'c1',
+          date: new Date('2025-10-01'),
+          amount: 1,
+          unit: ' L ',
+        },
+      ]);
+
+      const result = await service.feeding();
+
+      expect(result.byUnit).toEqual({
+        l: { byColony: { c1: 6 }, bySeason: { '2025': 6 } },
+        kg: { byColony: { c1: 2 }, bySeason: { '2025': 2 } },
+      });
+    });
   });
 });

ApiCore-Backend/src/statistics/statistics.service.ts

@@ -206,15 +206,27 @@ export class StatisticsService {
       select: { colonyId: true, date: true, amount: true, unit: true },
     });
 
+    // Litres and kilograms cannot be added up: totals are kept per unit
+    // (byUnit). byColony/bySeason stay for older clients and are only
+    // meaningful when a single unit is in use.
     const byColony: Record<string, number> = {};
     const bySeason: Record<string, number> = {};
+    const byUnit: Record<
+      string,
+      { byColony: Record<string, number>; bySeason: Record<string, number> }
+    > = {};
     for (const feeding of feedings) {
+      const year = feeding.date.getFullYear().toString();
+      const unit = feeding.unit.trim().toLowerCase() || 'ohne Einheit';
       byColony[feeding.colonyId] =
         (byColony[feeding.colonyId] ?? 0) + feeding.amount;
-      const year = feeding.date.getFullYear().toString();
       bySeason[year] = (bySeason[year] ?? 0) + feeding.amount;
+      const totals = (byUnit[unit] ??= { byColony: {}, bySeason: {} });
+      totals.byColony[feeding.colonyId] =
+        (totals.byColony[feeding.colonyId] ?? 0) + feeding.amount;
+      totals.bySeason[year] = (totals.bySeason[year] ?? 0) + feeding.amount;
     }
 
-    return { byColony, bySeason };
+    return { byColony, bySeason, byUnit };
   }
 }