test(audit): add cross-user scoping regression for youParticipated

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

backend/src/test/java/org/raddatz/familienarchiv/dashboard/AuditLogQueryRepositoryRolledUpTest.java

@@ -230,6 +230,21 @@ class AuditLogQueryRepositoryRolledUpTest {
         );
     }
 
+    @Test
+    void youParticipated_is_false_when_reply_notification_belongs_to_other_user() {
+        insertUserAndDocs();
+        UUID commentId = UUID.randomUUID();
+        insertAuditEvent(OTHER_USER_ID, DOC_ID, "COMMENT_ADDED",
+                Instant.parse("2026-04-20T10:00:00Z"), Map.of("commentId", commentId.toString()));
+        insertReplyNotification(OTHER_USER_ID, DOC_ID, commentId);
+
+        List<ActivityFeedRow> rows = auditLogQueryRepository.findRolledUpActivityFeed(USER_ID.toString(), 40);
+
+        assertThat(rows).allSatisfy(r ->
+                assertThat(r.isYouParticipated()).isFalse()
+        );
+    }
+
     @Test
     void youMentioned_is_true_when_mention_created_payload_matches_current_user() {
         insertUserAndDocs();