style(im/registrationInvite): 调整绑定用户提示的插槽封装与样式

将绑定用户未验证提示调整为插槽形式，并移除冗余的样式配置

web/src/views/im/registrationInvite/CreateModal.vue

@@ -20,7 +20,9 @@
           <span class="bound-user-name">{{ boundUser.nickname || boundUser.username || boundUser.phone || '--' }}（{{ boundUser.userId }}）</span>
           <n-button text type="error" @click="clearBoundUser">清除</n-button>
         </div>
-        <div v-if="bindInputUnverified" class="bind-user-tip">输入的用户ID未验证，请先点击搜索</div>
+        <template #feedback>
+          <div v-if="bindInputUnverified" class="bind-user-tip">输入的用户ID未验证，请先点击搜索</div>
+        </template>
       </n-form-item>
       <n-form-item label="到期时间" path="expiresAt">
         <n-date-picker v-model:value="formValue.expiresAt" type="datetime" clearable />
@@ -192,8 +194,6 @@
   }
 
   .bind-user-tip {
-    width: 100%;
-    margin-top: 4px;
     color: #f0a020;
     font-size: 12px;
   }