feat(search-result): extend DocumentSearchResult with pageNumber/pageSize/totalPages

Rename `total` → `totalElements` for Spring-Page parity and add three new
required paging fields: pageNumber, pageSize, totalPages. Adds a `paged(
slice, pageable, totalElements)` factory alongside the existing single-page
`of(list)` shortcut. Enables offset pagination of /documents search (#315).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/dto/DocumentSearchResult.java

@@ -1,6 +1,7 @@
 package org.raddatz.familienarchiv.dto;
 
 import io.swagger.v3.oas.annotations.media.Schema;
+import org.springframework.data.domain.Pageable;
 
 import java.util.List;
 
@@ -8,9 +9,30 @@ public record DocumentSearchResult(
         @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
         List<DocumentSearchItem> items,
         @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
-        long total
+        long totalElements,
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+        int pageNumber,
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+        int pageSize,
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+        int totalPages
 ) {
+    /**
+     * Single-page convenience factory used by empty-result shortcuts and by tests that
+     * don't care about paging. Treats the whole list as page 0 of itself.
+     */
     public static DocumentSearchResult of(List<DocumentSearchItem> items) {
-        return new DocumentSearchResult(items, items.size());
+        int size = items.size();
+        return new DocumentSearchResult(items, size, 0, size, size == 0 ? 0 : 1);
+    }
+
+    /**
+     * Paged factory used by the service when it has a real Pageable + full match count
+     * (e.g. from Spring's Page<T> or from an in-memory sort-then-slice).
+     */
+    public static DocumentSearchResult paged(List<DocumentSearchItem> slice, Pageable pageable, long totalElements) {
+        int pageSize = pageable.getPageSize();
+        int totalPages = pageSize == 0 ? 0 : (int) ((totalElements + pageSize - 1) / pageSize);
+        return new DocumentSearchResult(slice, totalElements, pageable.getPageNumber(), pageSize, totalPages);
     }
 }

backend/src/test/java/org/raddatz/familienarchiv/dto/DocumentSearchResultTest.java

@@ -5,6 +5,7 @@ import org.junit.jupiter.api.Test;
 import org.raddatz.familienarchiv.audit.ActivityActorDTO;
 import org.raddatz.familienarchiv.model.Document;
 import org.raddatz.familienarchiv.model.DocumentStatus;
+import org.springframework.data.domain.PageRequest;
 
 import java.util.List;
 import java.util.UUID;
@@ -24,10 +25,43 @@ class DocumentSearchResultTest {
     }
 
     @Test
-    void of_total_equals_list_size() {
-        DocumentSearchResult result = DocumentSearchResult.of(List.of(item(UUID.randomUUID()), item(UUID.randomUUID())));
+    void of_totalElements_equals_list_size_for_unpaged_shortcut() {
+        DocumentSearchResult result = DocumentSearchResult.of(
+                List.of(item(UUID.randomUUID()), item(UUID.randomUUID())));
 
-        assertThat(result.total()).isEqualTo(2L);
+        assertThat(result.totalElements()).isEqualTo(2L);
+        assertThat(result.pageNumber()).isZero();
+        assertThat(result.pageSize()).isEqualTo(2);
+        assertThat(result.totalPages()).isEqualTo(1);
+    }
+
+    @Test
+    void of_empty_shortcut_has_zero_totalPages() {
+        DocumentSearchResult result = DocumentSearchResult.of(List.of());
+
+        assertThat(result.totalElements()).isZero();
+        assertThat(result.totalPages()).isZero();
+    }
+
+    @Test
+    void paged_factory_populates_paging_fields_from_pageable_and_total() {
+        List<DocumentSearchItem> slice = List.of(item(UUID.randomUUID()), item(UUID.randomUUID()));
+
+        DocumentSearchResult result = DocumentSearchResult.paged(slice, PageRequest.of(1, 50), 120L);
+
+        assertThat(result.items()).hasSize(2);
+        assertThat(result.totalElements()).isEqualTo(120L);
+        assertThat(result.pageNumber()).isEqualTo(1);
+        assertThat(result.pageSize()).isEqualTo(50);
+        assertThat(result.totalPages()).isEqualTo(3); // ceil(120 / 50)
+    }
+
+    @Test
+    void paged_factory_totalPages_rounds_up_on_remainder() {
+        DocumentSearchResult result =
+                DocumentSearchResult.paged(List.of(), PageRequest.of(0, 7), 30L);
+
+        assertThat(result.totalPages()).isEqualTo(5); // ceil(30 / 7)
     }
 
     @Test
@@ -53,9 +87,18 @@ class DocumentSearchResultTest {
     }
 
     @Test
-    void total_component_is_annotated_as_required_in_openapi_schema() throws NoSuchFieldException {
-        Schema schema = DocumentSearchResult.class.getDeclaredField("total").getAnnotation(Schema.class);
+    void totalElements_component_is_annotated_as_required_in_openapi_schema() throws NoSuchFieldException {
+        Schema schema = DocumentSearchResult.class.getDeclaredField("totalElements").getAnnotation(Schema.class);
         assertThat(schema).isNotNull();
         assertThat(schema.requiredMode()).isEqualTo(Schema.RequiredMode.REQUIRED);
     }
+
+    @Test
+    void paging_components_are_annotated_as_required_in_openapi_schema() throws NoSuchFieldException {
+        for (String name : List.of("pageNumber", "pageSize", "totalPages")) {
+            Schema schema = DocumentSearchResult.class.getDeclaredField(name).getAnnotation(Schema.class);
+            assertThat(schema).as(name + " must have @Schema").isNotNull();
+            assertThat(schema.requiredMode()).isEqualTo(Schema.RequiredMode.REQUIRED);
+        }
+    }
 }