feat(community): add getAllMemberships() to MembershipService

Add @Transactional(readOnly = true) method that uses findAllWithDetails()
and batch-fetches users with the same lookup pattern as getPendingMemberships().
Returns List<PendingMembershipResponse> with all memberships (pending, active,
inactive) for the admin overview tab.

Tests: 3 new tests covering normal case, empty list, and missing user.

eeg_backend/src/main/java/at/mueller/eeg/backend/community/service/MembershipService.java

@@ -143,6 +143,37 @@ public class MembershipService {
                 .toList();
     }
 
+    @Transactional(readOnly = true)
+    public List<PendingMembershipResponse> getAllMemberships() {
+        List<Membership> allMemberships = membershipRepository.findAllWithDetails();
+
+        List<UUID> userIds = allMemberships.stream()
+                .map(m -> m.getMeteringPoint().getUserId())
+                .distinct()
+                .toList();
+
+        Map<UUID, User> usersById = userRepository.findAllById(userIds).stream()
+                .collect(Collectors.toMap(User::getId, user -> user));
+
+        return allMemberships.stream()
+                .map(m -> {
+                    User user = usersById.get(m.getMeteringPoint().getUserId());
+                    return new PendingMembershipResponse(
+                            m.getId(),
+                            user != null ? user.getEmail() : "unknown",
+                            user != null ? user.getFirstName() : "unknown",
+                            user != null ? user.getLastName() : "unknown",
+                            m.getMeteringPoint().getAtNumber(),
+                            m.getEnergyCommunity().getName(),
+                            m.getPriorityLevel(),
+                            m.getStatus().name(),
+                            m.getValidFrom(),
+                            m.getValidTo()
+                    );
+                })
+                .toList();
+    }
+
     @Transactional(readOnly = true)
     public List<PendingMembershipResponse> getPendingMemberships() {
         List<Membership> pendingMemberships = membershipRepository.findPendingWithDetails();

eeg_backend/src/test/java/at/mueller/eeg/backend/community/service/MembershipServiceTest.java

@@ -259,6 +259,48 @@ class MembershipServiceTest {
         assertNull(result.get(0).validTo());
     }
 
+    @Test
+    void getAllMemberships_returnsAllMemberships() {
+        when(membershipRepository.findAllWithDetails()).thenReturn(List.of(testMembership));
+        when(userRepository.findAllById(List.of(testUserId))).thenReturn(List.of(testUser));
+
+        List<PendingMembershipResponse> result = membershipService.getAllMemberships();
+
+        assertEquals(1, result.size());
+        assertEquals(testMembershipId, result.get(0).id());
+        assertEquals("test@example.com", result.get(0).userEmail());
+        assertEquals("Test", result.get(0).firstName());
+        assertEquals("PENDING", result.get(0).status());
+    }
+
+    @Test
+    void getAllMemberships_returnsEmptyListWhenNoMemberships() {
+        when(membershipRepository.findAllWithDetails()).thenReturn(List.of());
+
+        List<PendingMembershipResponse> result = membershipService.getAllMemberships();
+
+        assertTrue(result.isEmpty());
+        verify(userRepository).findAllById(List.of());
+    }
+
+    @Test
+    void getAllMemberships_handlesMissingUser() {
+        Membership membershipWithUnknownUser = new Membership();
+        membershipWithUnknownUser.setId(UUID.randomUUID());
+        membershipWithUnknownUser.setMeteringPoint(testMeteringPoint);
+        membershipWithUnknownUser.setEnergyCommunity(testCommunity);
+        membershipWithUnknownUser.setPriorityLevel(1);
+        membershipWithUnknownUser.setStatus(MembershipStatus.ACTIVE);
+
+        when(membershipRepository.findAllWithDetails()).thenReturn(List.of(membershipWithUnknownUser));
+        when(userRepository.findAllById(List.of(testUserId))).thenReturn(List.of());
+
+        List<PendingMembershipResponse> result = membershipService.getAllMemberships();
+
+        assertEquals(1, result.size());
+        assertEquals("unknown", result.get(0).userEmail());
+    }
+
     @Test
     void getPendingMemberships_setsValidDatesFromEntity() {
         testMembership.setStatus(MembershipStatus.ACTIVE);