fix(db): users 테이블의 닉네임은 lowercase 로 index

init/sql/init.sql

@@ -4,11 +4,13 @@ CREATE USER wsd WITH PASSWORD 'wsdpass1234';
 CREATE TABLE users (
     id                      SERIAL NOT NULL PRIMARY KEY, /* SERIAL is denoted as INTEGER when referencing */
     email                   VARCHAR(64) NOT NULL UNIQUE,
-    nickname                VARCHAR(16) NOT NULL UNIQUE,
+    nickname                VARCHAR(16) NOT NULL,
     password                VARCHAR(64) NOT NULL,
     created_at              TIMESTAMP NOT NULL DEFAULT NOW()
 );
 
+CREATE UNIQUE INDEX users_nickname_key ON users (LOWER(nickname));
+
 CREATE TYPE part_type AS ENUM ('ETC', 'CPU', 'RAM', 'MB', 'GPU', 'SSD', 'HDD');
 
 CREATE TABLE parts (