feat(search): wrap search response in { documents, total } envelope

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

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

@@ -91,6 +91,18 @@ class DocumentControllerTest {
                 .andExpect(status().isBadRequest());
     }
 
+    @Test
+    @WithMockUser
+    void search_responseContainsTotalCount() throws Exception {
+        when(documentService.searchDocuments(any(), any(), any(), any(), any(), any(), any(), any(), any(), any()))
+                .thenReturn(Collections.emptyList());
+
+        mockMvc.perform(get("/api/documents/search"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.total").value(0))
+                .andExpect(jsonPath("$.documents").isArray());
+    }
+
     // ─── POST /api/documents ─────────────────────────────────────────────────
 
     @Test