feat(documents): V53 add thumbnail_aspect + page_count columns

Adds two nullable metadata columns to documents, populated by
ThumbnailService when it generates the JPEG preview. Both remain null
until the existing admin backfill endpoint reruns the service.

Refs #305

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

backend/src/test/java/org/raddatz/familienarchiv/repository/MigrationIntegrationTest.java

@@ -302,6 +302,51 @@ class MigrationIntegrationTest {
         ).isInstanceOf(DataIntegrityViolationException.class);
     }
 
+    // ─── V53: add thumbnail_aspect + page_count columns to documents ─────────
+
+    @Test
+    void v53_thumbnailAspectColumn_existsAndIsNullable() {
+        UUID docId = createDocument();
+
+        // Column must exist and accept NULL (freshly-created doc has no thumbnail yet)
+        String aspect = jdbc.queryForObject(
+                "SELECT thumbnail_aspect FROM documents WHERE id = ?", String.class, docId);
+        assertThat(aspect).isNull();
+    }
+
+    @Test
+    void v53_pageCountColumn_existsAndIsNullable() {
+        UUID docId = createDocument();
+
+        Integer pageCount = jdbc.queryForObject(
+                "SELECT page_count FROM documents WHERE id = ?", Integer.class, docId);
+        assertThat(pageCount).isNull();
+    }
+
+    @Test
+    void v53_thumbnailAspectColumn_acceptsPortraitAndLandscape() {
+        UUID docId = createDocument();
+
+        int portraitRows = jdbc.update(
+                "UPDATE documents SET thumbnail_aspect = 'PORTRAIT' WHERE id = ?", docId);
+        assertThat(portraitRows).isEqualTo(1);
+
+        int landscapeRows = jdbc.update(
+                "UPDATE documents SET thumbnail_aspect = 'LANDSCAPE' WHERE id = ?", docId);
+        assertThat(landscapeRows).isEqualTo(1);
+    }
+
+    @Test
+    void v53_pageCountColumn_storesInteger() {
+        UUID docId = createDocument();
+
+        jdbc.update("UPDATE documents SET page_count = 4 WHERE id = ?", docId);
+
+        Integer stored = jdbc.queryForObject(
+                "SELECT page_count FROM documents WHERE id = ?", Integer.class, docId);
+        assertThat(stored).isEqualTo(4);
+    }
+
     // ─── V51: backfill annotation_id on block comments and notifications ─────
 
     @Test