feat: 支持注销用户并展示普通用户使用情况

- 新增管理员注销用户接口，要求输入用户名二次确认
- 注销时清理用户当前图片、视频、文件、标签、会话和自身日志
- 保留备份任务、管理员审计数据和全局配置
- 用户列表展示图片、视频、文件占用，管理员行隐藏使用情况和操作按钮
- 补充注销流程与用量统计测试

i18n/locales/en.json

@@ -1283,14 +1283,25 @@
   ,
   "users": {
     "title": "Users",
-    "subtitle": "Review accounts and clear passwords; users set a new one on next login",
+    "subtitle": "Review accounts, clear passwords, or delete users",
     "adminOnly": "Admins only",
     "roleAdmin": "Admin",
     "roleUser": "User",
     "clearPassword": "Clear password",
+    "deleteUser": "Delete user",
+    "usageImages": "Images",
+    "usageVideos": "Videos",
+    "usageFiles": "Files",
     "resetPending": "Reset pending",
     "passwordCleared": "Cleared password for {name}",
     "clearFailed": "Operation failed",
+    "deleteTitle": "Delete user?",
+    "deleteWarning": "This permanently deletes the user's current images, videos, files, tags, and login sessions. Admin and other users' data are not affected. This cannot be undone.",
+    "deleteConfirmLabel": "Type the username {name} to confirm",
+    "deleteSubmit": "Delete user",
+    "deleteFailed": "Delete failed",
+    "userDeleted": "Deleted user {name}",
+    "adminProtected": "Admin accounts cannot be cleared or deleted",
     "loadFailed": "Failed to load users"
   },
   "reset": {

i18n/locales/zh-CN.json

@@ -1286,14 +1286,25 @@
   ,
   "users": {
     "title": "用户管理",
-    "subtitle": "查看账号并清除密码，用户下次登录时重新设置",
+    "subtitle": "查看账号、清除密码或注销用户",
     "adminOnly": "仅管理员可访问此页面",
     "roleAdmin": "管理员",
     "roleUser": "普通用户",
     "clearPassword": "清除密码",
+    "deleteUser": "注销用户",
+    "usageImages": "图片",
+    "usageVideos": "视频",
+    "usageFiles": "文件",
     "resetPending": "待重置密码",
     "passwordCleared": "已清除 {name} 的密码",
     "clearFailed": "操作失败",
+    "deleteTitle": "注销用户？",
+    "deleteWarning": "将永久删除该用户当前的图片、视频、文件、标签和登录会话。管理员数据和其他用户数据不受影响，此操作不可恢复。",
+    "deleteConfirmLabel": "输入用户名 {name} 确认注销",
+    "deleteSubmit": "确认注销",
+    "deleteFailed": "注销失败",
+    "userDeleted": "已注销用户 {name}",
+    "adminProtected": "管理员账号不可清除密码或注销",
     "loadFailed": "读取用户列表失败"
   },
   "reset": {