refactor: worker_id 잔재 제거 - user_id 기반으로 완전 전환

- workerModel: remove()를 user_id 기반 cascading delete로 전환
- workerController: 계정 생성/해제를 workers.user_id 연결 방식으로 변경
- userController: JOIN 방향 전환 (u.worker_id→w.worker_id 에서 w.user_id→u.user_id)
- authController, systemController, authRoutes: 모든 CRUD에서 worker_id 참조 제거
- DB: UNIQUE KEY 5개 교체, FK 7개 삭제, daily_worker_summary user_id 추가

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

system1-factory/api/controllers/systemController.js

@@ -243,21 +243,20 @@ exports.getAllUsers = asyncHandler(async (req, res) => {
     const db = await getDb();
     
     const [users] = await db.query(`
-      SELECT 
+      SELECT
         user_id,
         username,
         name,
         email,
         role,
         access_level,
-        worker_id,
         is_active,
         last_login_at,
         failed_login_attempts,
         locked_until,
         created_at,
         updated_at
-      FROM users 
+      FROM users
       ORDER BY created_at DESC
     `);
     
@@ -272,20 +271,20 @@ exports.getAllUsers = asyncHandler(async (req, res) => {
  * 사용자 생성
  */
 exports.createUser = asyncHandler(async (req, res) => {
-  const { username, password, name, email, role, access_level, worker_id } = req.body;
-  
+  const { username, password, name, email, role, access_level } = req.body;
+
   // 스키마 기반 유효성 검사
   validateSchema(req.body, schemas.createUser);
-  
+
   try {
     const db = await getDb();
-    
+
     // 사용자명 중복 확인
     const [existing] = await db.query('SELECT user_id FROM users WHERE username = ?', [username]);
     if (existing.length > 0) {
       throw new ApiError('이미 존재하는 사용자명입니다.', 409);
     }
-    
+
     // 이메일 중복 확인 (이메일이 제공된 경우)
     if (email) {
       const [existingEmail] = await db.query('SELECT user_id FROM users WHERE email = ?', [email]);
@@ -293,15 +292,15 @@ exports.createUser = asyncHandler(async (req, res) => {
         throw new ApiError('이미 사용 중인 이메일입니다.', 409);
       }
     }
-    
+
     // 비밀번호 해시화
     const hashedPassword = await bcrypt.hash(password, 10);
-    
+
     // 사용자 생성
     const [result] = await db.query(`
-      INSERT INTO users (username, password, name, email, role, access_level, worker_id, is_active, created_at, password_changed_at) 
-      VALUES (?, ?, ?, ?, ?, ?, ?, 1, NOW(), NOW())
-    `, [username, hashedPassword, name, email || null, role, access_level || role, worker_id || null]);
+      INSERT INTO users (username, password, name, email, role, access_level, is_active, created_at, password_changed_at)
+      VALUES (?, ?, ?, ?, ?, ?, 1, NOW(), NOW())
+    `, [username, hashedPassword, name, email || null, role, access_level || role]);
     
     // 비밀번호 변경 로그 기록
     await db.query(`
@@ -322,9 +321,9 @@ exports.createUser = asyncHandler(async (req, res) => {
 exports.updateUser = async (req, res) => {
   try {
     const { id } = req.params;
-    const { name, email, role, access_level, is_active, worker_id } = req.body;
+    const { name, email, role, access_level, is_active } = req.body;
     const db = await getDb();
-    
+
     // 사용자 존재 확인
     const [user] = await db.query('SELECT user_id FROM users WHERE user_id = ?', [id]);
     if (user.length === 0) {
@@ -333,11 +332,11 @@ exports.updateUser = async (req, res) => {
         error: '해당 사용자를 찾을 수 없습니다.'
       });
     }
-    
+
     // 이메일 중복 확인 (다른 사용자가 사용 중인지)
     if (email) {
       const [existingEmail] = await db.query(
-        'SELECT user_id FROM users WHERE email = ? AND user_id != ?', 
+        'SELECT user_id FROM users WHERE email = ? AND user_id != ?',
         [email, id]
       );
       if (existingEmail.length > 0) {
@@ -347,13 +346,13 @@ exports.updateUser = async (req, res) => {
         });
       }
     }
-    
+
     // 사용자 정보 업데이트
     await db.query(`
-      UPDATE users 
-      SET name = ?, email = ?, role = ?, access_level = ?, is_active = ?, worker_id = ?, updated_at = NOW()
+      UPDATE users
+      SET name = ?, email = ?, role = ?, access_level = ?, is_active = ?, updated_at = NOW()
       WHERE user_id = ?
-    `, [name, email || null, role, access_level || role, is_active ? 1 : 0, worker_id || null, id]);
+    `, [name, email || null, role, access_level || role, is_active ? 1 : 0, id]);
     
     res.json({
       success: true,