fix(document): add receivers+trainingLabels to Document.list entity graph

Document.list was missing receivers (caused LazyInitializationException
when sorting by receiver) and trainingLabels (latent crash for any
document with OCR training labels assigned). Document.full was missing
trainingLabels for the same reason. OSIV is disabled so every lazy
association used after the transaction closes must be in the graph.

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

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

@@ -25,11 +25,14 @@ import java.util.UUID;
 @NamedEntityGraph(name = "Document.full", attributeNodes = {
         @NamedAttributeNode("sender"),
         @NamedAttributeNode("receivers"),
-        @NamedAttributeNode("tags")
+        @NamedAttributeNode("tags"),
+        @NamedAttributeNode("trainingLabels")
 })
 @NamedEntityGraph(name = "Document.list", attributeNodes = {
         @NamedAttributeNode("sender"),
-        @NamedAttributeNode("tags")
+        @NamedAttributeNode("receivers"),
+        @NamedAttributeNode("tags"),
+        @NamedAttributeNode("trainingLabels")
 })
 @Entity
 @Table(name = "documents")