Create fsrs upadte method

sql/card_stats.sql

@@ -10,8 +10,7 @@ create table card_stats
             on delete cascade,
     score       INTEGER default 1 not null,
     last_opened INTEGER           not null,
-    added INTEGER not null,
-    fsrs_opened INTEGER,
-    fsrs_memory INTEGER,
-    fsrs_open_time INTEGER
+    fsrs_opened INTEGER not null,
+    fsrs_memory INTEGER not null,
+    fsrs_open_day INTEGER not null
 );