* 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.
