✨ feat: add admin-only "remark" support for users

* backend
  - model: add `Remark` field (varchar 255, `json:"remark,omitempty"`); AutoMigrate handles schema change automatically
  - controller:
    * accept `remark` on user create/update endpoints
    * hide remark from regular users (`GetSelf`) by zero-ing the field before JSON marshalling
    * clarify inline comment explaining the omitempty behaviour

* frontend (React / Semi UI)
  - AddUser.js & EditUser.js: add “Remark” input for admins
  - UsersTable.js:
    * remove standalone “Remark” column
    * show remark as a truncated Tag next to username with Tooltip for full text
    * import Tooltip component
  - i18n: reuse existing translations where applicable

This commit enables administrators to label users with private notes while ensuring those notes are never exposed to the users themselves.

web/src/components/table/UsersTable.js

@@ -26,6 +26,7 @@ import {
   Space,
   Table,
   Tag,
+  Tooltip,
   Typography
 } from '@douyinfe/semi-ui';
 import {
@@ -110,6 +111,27 @@ const UsersTable = () => {
     {
       title: t('用户名'),
       dataIndex: 'username',
+      render: (text, record) => {
+        const remark = record.remark;
+        if (!remark) {
+          return <span>{text}</span>;
+        }
+        const maxLen = 10;
+        const displayRemark = remark.length > maxLen ? remark.slice(0, maxLen) + '…' : remark;
+        return (
+          <Space spacing={2}>
+            <span>{text}</span>
+            <Tooltip content={remark} position="top" showArrow>
+              <Tag color='white' size='large' shape='circle' className="!text-xs">
+                <div className="flex items-center gap-1">
+                  <div className="w-2 h-2 rounded-full flex-shrink-0" style={{ backgroundColor: '#10b981' }} />
+                  {displayRemark}
+                </div>
+              </Tag>
+            </Tooltip>
+          </Space>
+        );
+      },
     },
     {
       title: t('分组'),