add employee service functions for CRUD operations

src/services/employee.ts

+import http from './http'
+import type { Employee } from '@/types/Employee'
+
+export async function listEmployees(): Promise<Employee[]> {
+  const { data } = await http.get('/employees')
+  return data
+}
+
+export async function getEmployee(id: number): Promise<Employee> {
+  const { data } = await http.get(`/employees/${id}`)
+  return data
+}
+
+export async function createEmployee(payload: Partial<Employee>): Promise<Employee> {
+  const { data } = await http.post('/employees', payload)
+  return data
+}
+
+export async function updateEmployee(id: number, payload: Partial<Employee>): Promise<Employee> {
+  const { data } = await http.put(`/employees/${id}`, payload)
+  return data
+}
+
+export async function deleteEmployee(id: number): Promise<void> {
+  await http.delete(`/employees/${id}`)
+}