refactor: [hr] 사번(employee_code) 필드 전체 제거

- Model: appends, accessor 제거
- Service: 검색 필터, json_extra 저장/수정 로직 제거
- Controller: validation 규칙 제거
- View: create, edit, show, table에서 사번 UI 제거

app/Http/Controllers/Api/Admin/HR/EmployeeController.php

@@ -85,7 +85,6 @@ public function store(Request $request): JsonResponse
             'employee_status' => 'nullable|string|in:active,leave,resigned',
             'manager_user_id' => 'nullable|integer|exists:users,id',
             'display_name' => 'nullable|string|max:50',
-            'employee_code' => 'nullable|string|max:30',
             'hire_date' => 'nullable|date',
             'address' => 'nullable|string|max:200',
             'emergency_contact' => 'nullable|string|max:100',
@@ -154,7 +153,6 @@ public function update(Request $request, int $id): JsonResponse
             'employee_status' => 'nullable|string|in:active,leave,resigned',
             'manager_user_id' => 'nullable|integer|exists:users,id',
             'display_name' => 'nullable|string|max:50',
-            'employee_code' => 'nullable|string|max:30',
             'hire_date' => 'nullable|date',
             'address' => 'nullable|string|max:200',
             'emergency_contact' => 'nullable|string|max:100',