refactored scheme

backend/schemeV2.mock_data.sql

@@ -1,3 +1,5 @@
+-- MUST BE UPDATED BEFORE USE
+
 USE borrow_system_new;
 
 -- Optional: keep insert order predictable

backend/schemeV2.sql

@@ -25,6 +25,7 @@ CREATE TABLE loans (
   loaned_items_id json NOT NULL DEFAULT ('[]'),
   loaned_items_name json NOT NULL DEFAULT ('[]'),
   deleted bool NOT NULL DEFAULT false,
+  note varchar(500) DEFAULT NULL,
   PRIMARY KEY (id),
   CONSTRAINT fk_loans_username
     FOREIGN KEY (username) REFERENCES users(username)