feat: login service and implement database storage

internal/domain/auth/staff.go

@@ -0,0 +1,10 @@
+package domain
+
+type StaffLoginReq struct {
+	Email    string `json:"email" validate:"required"`
+	Password string `json:"password" validate:"required"`
+}
+
+type StaffLoginResponse struct {
+	Token string `json:"token"`
+}