fix(backend): IDOR in POST /notifications/:id/read (Modul 26)

markRead() pruefte bisher nicht, ob die Benachrichtigung dem
anfragenden Nutzer gehoert - jeder authentifizierte Nutzer konnte
fremde Benachrichtigungen als gelesen markieren. Jetzt: 403 bei
fremder Benachrichtigung, weiterhin erlaubt fuer eigene und
Broadcast-Benachrichtigungen (userId = null). E2E-Regressionstest
ergaenzt.

ApiCore-Backend/test/notifications.e2e-spec.ts

@@ -17,8 +17,11 @@ describe('Notifications (e2e)', () => {
   let prisma: PrismaService;
   const beekeeperEmail = `notifications-e2e-beekeeper-${Date.now()}@example.com`;
   const password = 'SuperSecret123!';
+  const staffEmail = `notifications-e2e-staff-${Date.now()}@example.com`;
   let beekeeperId: string;
+  let staffId: string;
   let beekeeperToken: string;
+  let staffToken: string;
   let notificationId: string;
 
   beforeAll(async () => {
@@ -35,7 +38,12 @@ describe('Notifications (e2e)', () => {
       },
     });
     beekeeperId = beekeeper.id;
+    const staff = await prisma.user.create({
+      data: { email: staffEmail, passwordHash, name: 'Staff', role: 'STAFF' },
+    });
+    staffId = staff.id;
     beekeeperToken = (await login(app, beekeeperEmail, password)).accessToken;
+    staffToken = (await login(app, staffEmail, password)).accessToken;
 
     const notification = await prisma.notification.create({
       data: {
@@ -49,9 +57,15 @@ describe('Notifications (e2e)', () => {
 
   afterAll(async () => {
     await prisma.notification.deleteMany({ where: { id: notificationId } });
-    await prisma.refreshToken.deleteMany({ where: { userId: beekeeperId } });
-    await prisma.auditLog.deleteMany({ where: { userId: beekeeperId } });
-    await prisma.user.deleteMany({ where: { id: beekeeperId } });
+    await prisma.refreshToken.deleteMany({
+      where: { userId: { in: [beekeeperId, staffId] } },
+    });
+    await prisma.auditLog.deleteMany({
+      where: { userId: { in: [beekeeperId, staffId] } },
+    });
+    await prisma.user.deleteMany({
+      where: { id: { in: [beekeeperId, staffId] } },
+    });
     await app.close();
   });
 
@@ -70,6 +84,13 @@ describe('Notifications (e2e)', () => {
     ).toBe(true);
   });
 
+  it("rejects marking another user's notification as read", () => {
+    return request(app.getHttpServer())
+      .post(`/api/v1/notifications/${notificationId}/read`)
+      .set('Authorization', `Bearer ${staffToken}`)
+      .expect(403);
+  });
+
   it('marks a notification as read', async () => {
     const response = await request(app.getHttpServer())
       .post(`/api/v1/notifications/${notificationId}/read`)