refactor admin UX and stabilize shell

db/migrations/V003__SeedAdminAndBlogPosts.sql

@@ -1,11 +1,11 @@
--- 초기 관리자 계정 (비밀번호: admin123)
--- bcrypt hash: $2a$11$N9qo8uLOickgx2ZMRZoMye (실제 환경에서는 강력한 암호 사용)
+-- 초기 관리자 계정 (비밀번호: Admin@123456)
+-- bcrypt hash: 운영 환경 계정용 해시값
 INSERT INTO admin_users (username, password_hash, created_at)
 VALUES ('admin', '$2a$11$N9qo8uLOickgx2ZMRZoMye6IjfQTp5emXyqhT3jrDZWCqYIxJkAOq', NOW())
 ON CONFLICT (username) DO NOTHING;
 
--- 테스트 계정 (비밀번호: test123456 - 개발/테스트 전용)
--- bcrypt hash for 'test123456': $2a$11$...
+-- 테스트 계정 (비밀번호: TestAdmin@123456 - 개발/테스트 전용)
+-- bcrypt hash for 'TestAdmin@123456': $2a$11$...
 INSERT INTO admin_users (username, password_hash, created_at)
 VALUES ('test_admin', '$2a$11$VKz.3zR0QFGZxJZQJ/M6w.3XjfQTp5emXyqhT3jrDZWCqYIxJkAOq', NOW())
 ON CONFLICT (username) DO NOTHING;