Restore unread baseline and read tracking

SHiNE-server/shine-server-net-protocol/src/main/java/server/logic/ws_protocol/JSON/handlers/channels/ChannelsReadSupport.java

@@ -161,7 +161,7 @@ final class ChannelsReadSupport {
               AND setting_key = ?
             LIMIT 1
             """;
-        long lastSeen = 0;
+        long lastSeen = messagesCount;
         try (PreparedStatement ps = c.prepareStatement(sql)) {
             ps.setString(1, viewerLogin);
             ps.setInt(2, 1);