A notifications marker reads what it passes

Saving the notifications marker (/api/v1/markers) moved the marker but left
every notification unread, so a Mastodon client's unread count never fell.
The marker now marks read every notification up to it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

PrivaPub/Api/Mastodon/Controllers/TimelinesController.cs

@@ -146,6 +146,10 @@ namespace PrivaPub.Api.Mastodon.Controllers
 					.Option(o => o.IsUpsert = true)
 					.ExecuteAsync(token);
 				result[timeline] = new Entities.Marker { LastReadId = marker.LastReadId, Version = marker.Version, UpdatedAt = MastodonJson.Time(marker.UpdatedAt) };
+				// what the marker passes is read: the unread count (v1 and v2) counts only what is newer
+				if (timeline == "notifications")
+					await DB.Default.Update<NotificationEntity>().Match(n => n.AvatarId == MyId && !n.IsRead)
+						.Match(f => f.Lte(n => n.ID, lastRead)).Modify(n => n.IsRead, true).ExecuteAsync(token);
 			}
 			return Json(result);
 		}