[O] Fix crash due to duplicate keys in maimai2_user_item

src/main/resources/db/migration/mariadb/V250__maimai2_item_integrity.sql

@@ -0,0 +1,4 @@
+# Fixes crashes due to duplicate keys in maimai2_user_item
+alter table maimai2_user_item
+    add constraint maimai2_user_item_pk
+        unique (item_kind, item_id, user_id);

src/main/resources/db/migration/mysql/V250__maimai2_item_integrity.sql

@@ -0,0 +1,4 @@
+# Fixes crashes due to duplicate keys in maimai2_user_item
+alter table maimai2_user_item
+    add constraint maimai2_user_item_pk
+        unique (item_kind, item_id, user_id);

src/main/resources/db/migration/sqlite/V250__maimai2_item_integrity.sql

@@ -0,0 +1 @@
+CREATE UNIQUE INDEX maimai2_user_item_pk ON maimai2_user_item(item_kind, item_id, user_id);