docs: explain stylesheet ownership, responsive rules and display boundaries

app/assets/styles/CaptchaField.BSN3ZbsD.css

@@ -1,3 +1,5 @@
+/* 图形验证码字段：输入、图片与换图行布局。 */
+/* 导入方：app/components/CaptchaField.vue、app/components/SecurityVerificationDialog.vue、app/components/instance/DcimActions.vue、app/components/instance/DcimBilling.vue、app/components/instance/DcimManage.vue、app/components/instance/InstanceAccess.vue、app/components/instance/InstanceBilling.vue、app/components/instance/InstanceSmsCode.vue、app/pages/account/index.vue、app/pages/forgot-password.vue、app/pages/login.vue、app/pages/oauth/bind.vue、app/pages/register.vue、app/pages/transfer/index.vue。 */
 .field[data-v-5ba6618f] {
   flex-direction: column;
   gap: 6px;