feat: Introduce knex for database migrations

- Adds knex.js to manage database schema changes systematically.
- Creates an initial migration file based on `hyungi_schema_v2.sql` to represent the current database state.
- Adds npm scripts (`db:migrate`, `db:rollback`, etc.) for easy execution of migration tasks.
- Archives legacy SQL files and old migration scripts into the `db_archive/` directory to prevent confusion and clean up the project structure.

api.hyungi.net/db_archive/migrations/006_add_description_column.sql

@@ -0,0 +1,16 @@
+-- 006_add_description_column.sql
+-- daily_work_reports 테이블에 description 컬럼 추가
+
+-- description 컬럼 추가 (이미 존재하는 경우 무시)
+SET @sql = (SELECT IF(
+    (SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS 
+     WHERE table_name = 'daily_work_reports' 
+     AND table_schema = 'hyungi' 
+     AND column_name = 'description') = 0,
+    'ALTER TABLE daily_work_reports ADD COLUMN description TEXT COMMENT ''작업 설명'' AFTER work_hours',
+    'SELECT ''description column already exists'' as message'
+));
+
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;