feat(documents): expose thumbnailAspect + pageCount on Document entity

Adds ThumbnailAspect enum (PORTRAIT | LANDSCAPE) and maps the two
nullable columns from V53 as JPA fields so ThumbnailService can
populate them and the API can return them unchanged to the frontend.

Refs #305

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

backend/src/main/java/org/raddatz/familienarchiv/model/Document.java

@@ -50,6 +50,13 @@ public class Document {
     @Column(name = "thumbnail_generated_at")
     private LocalDateTime thumbnailGeneratedAt;
 
+    @Enumerated(EnumType.STRING)
+    @Column(name = "thumbnail_aspect", length = 16)
+    private ThumbnailAspect thumbnailAspect;
+
+    @Column(name = "page_count")
+    private Integer pageCount;
+
     // Originaler Dateiname beim Upload (z.B. "Brief_Oma_1940.pdf")
     @Column(name = "original_filename", nullable = false)
     @Schema(requiredMode = Schema.RequiredMode.REQUIRED)

backend/src/main/java/org/raddatz/familienarchiv/model/ThumbnailAspect.java

@@ -0,0 +1,6 @@
+package org.raddatz.familienarchiv.model;
+
+public enum ThumbnailAspect {
+    PORTRAIT,
+    LANDSCAPE
+}