feat(bulk-edit): add GET /api/documents/ids endpoint

READ_ALL-gated endpoint returning all document UUIDs matching the same
filter parameters as /search, ignoring page/size. Powers the "Alle X
editieren" fast path so the bulk-edit page can replace the selection
with every match in one round-trip.

Refs #225

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/test/java/org/raddatz/familienarchiv/controller/DocumentControllerTest.java

@@ -1016,6 +1016,39 @@ class DocumentControllerTest {
         verify(documentService).applyBulkEditToDocument(eq(id2), any());
     }
 
+    // ─── GET /api/documents/ids ──────────────────────────────────────────────
+
+    @Test
+    void getDocumentIds_returns401_whenUnauthenticated() throws Exception {
+        mockMvc.perform(get("/api/documents/ids"))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    @WithMockUser(authorities = "READ_ALL")
+    void getDocumentIds_returns200_andDelegatesToService() throws Exception {
+        UUID id = UUID.randomUUID();
+        when(documentService.findIdsForFilter(any(), any(), any(), any(), any(), any(), any(), any(), any()))
+                .thenReturn(List.of(id));
+
+        mockMvc.perform(get("/api/documents/ids"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$[0]").value(id.toString()));
+    }
+
+    @Test
+    @WithMockUser(authorities = "READ_ALL")
+    void getDocumentIds_passesSenderIdParamToService() throws Exception {
+        UUID senderId = UUID.randomUUID();
+        when(documentService.findIdsForFilter(any(), any(), any(), eq(senderId), any(), any(), any(), any(), any()))
+                .thenReturn(List.of());
+
+        mockMvc.perform(get("/api/documents/ids").param("senderId", senderId.toString()))
+                .andExpect(status().isOk());
+
+        verify(documentService).findIdsForFilter(any(), any(), any(), eq(senderId), any(), any(), any(), any(), any());
+    }
+
     // ─── POST /api/documents/batch-metadata ──────────────────────────────────
 
     @Test

backend/src/test/java/org/raddatz/familienarchiv/service/DocumentServiceTest.java

@@ -2089,6 +2089,32 @@ class DocumentServiceTest {
         assertThat(doc.getDocumentLocation()).isEqualTo("NewLocation");
     }
 
+    // ─── findIdsForFilter ────────────────────────────────────────────────────
+
+    @Test
+    void findIdsForFilter_returnsAllMatchingIds_uncapped() {
+        Document d1 = Document.builder().id(UUID.randomUUID()).title("A").build();
+        Document d2 = Document.builder().id(UUID.randomUUID()).title("B").build();
+        when(documentRepository.findAll(any(org.springframework.data.jpa.domain.Specification.class)))
+                .thenReturn(List.of(d1, d2));
+
+        List<UUID> result = documentService.findIdsForFilter(
+                null, null, null, null, null, null, null, null, null);
+
+        assertThat(result).containsExactly(d1.getId(), d2.getId());
+    }
+
+    @Test
+    void findIdsForFilter_returnsEmpty_whenFtsHasNoMatches() {
+        when(documentRepository.findRankedIdsByFts("xyz")).thenReturn(List.of());
+
+        List<UUID> result = documentService.findIdsForFilter(
+                "xyz", null, null, null, null, null, null, null, null);
+
+        assertThat(result).isEmpty();
+        verify(documentRepository, never()).findAll(any(org.springframework.data.jpa.domain.Specification.class));
+    }
+
     // ─── batchMetadata ───────────────────────────────────────────────────────
 
     @Test