feat(backend): reactivate endpoint for dissolved colonies and inactive apiaries

Da fachliche Objekte nie hart geloescht werden (nur status +
deactivatedAt), fehlte bisher ein Weg, ein versehentlich aufgeloestes
Volk oder deaktivierten Bienenstand wieder zu aktivieren. Neue
POST :id/reactivate-Endpunkte setzen status zurueck auf ACTIVE und
loeschen deactivatedAt; ConflictException wenn bereits aktiv.

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

@@ -1,4 +1,4 @@
-import { NotFoundException } from '@nestjs/common';
+import { ConflictException, NotFoundException } from '@nestjs/common';
 import { ApiariesService } from './apiaries.service';
 import { PrismaService } from '../prisma/prisma.service';
 import { AuditLogService } from '../audit/audit-log.service';
@@ -75,4 +75,35 @@ describe('ApiariesService', () => {
       expect.objectContaining({ entityType: 'Apiary', action: 'DEACTIVATE' }),
     );
   });
+
+  it('reactivate throws ConflictException when already active', async () => {
+    prisma.apiary.findUnique.mockResolvedValue(existingApiary);
+    await expect(
+      service.reactivate('apiary-1', 'user-1'),
+    ).rejects.toBeInstanceOf(ConflictException);
+  });
+
+  it('reactivate sets status to ACTIVE and clears deactivatedAt', async () => {
+    prisma.apiary.findUnique.mockResolvedValue({
+      ...existingApiary,
+      status: 'INACTIVE',
+      deactivatedAt: new Date(),
+    });
+    prisma.apiary.update.mockResolvedValue({
+      ...existingApiary,
+      status: 'ACTIVE',
+      deactivatedAt: null,
+    });
+
+    const result = await service.reactivate('apiary-1', 'user-1');
+
+    expect(result.status).toBe('ACTIVE');
+    expect(prisma.apiary.update).toHaveBeenCalledWith({
+      where: { id: 'apiary-1' },
+      data: { status: 'ACTIVE', deactivatedAt: null },
+    });
+    expect(auditLog.record).toHaveBeenCalledWith(
+      expect.objectContaining({ entityType: 'Apiary', action: 'UPDATE' }),
+    );
+  });
 });