refactor: migrate wechat to user attributes and enhance users list

Migrate the hardcoded wechat field to the new extensible user
attributes system and improve the users management UI.

Migration:
- Add migration 019 to move wechat data to user_attribute_values
- Remove wechat field from User entity, DTOs, and API contracts
- Clean up wechat-related code from backend and frontend

UsersView enhancements:
- Add text labels to action buttons (Filter Settings, Column Settings,
  Attributes Config) for better UX
- Change status column to show colored dot + Chinese text instead of
  English text
- Add dynamic attribute columns support with batch loading
- Add column visibility settings with localStorage persistence
- Add filter settings modal for search and filter preferences
- Update i18n translations

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/i18n/locales/zh.ts

@@ -430,9 +430,7 @@ export default {
     administrator: '管理员',
     user: '用户',
     username: '用户名',
-    wechat: '微信号',
     enterUsername: '输入用户名',
-    enterWechat: '输入微信号',
     editProfile: '编辑个人资料',
     updateProfile: '更新资料',
     updating: '更新中...',
@@ -583,12 +581,10 @@ export default {
       email: '邮箱',
       password: '密码',
       username: '用户名',
-      wechat: '微信号',
       notes: '备注',
       enterEmail: '请输入邮箱',
       enterPassword: '请输入密码',
       enterUsername: '请输入用户名（选填）',
-      enterWechat: '请输入微信号（选填）',
       enterNotes: '请输入备注（仅管理员可见）',
       notesHint: '此备注仅对管理员可见',
       enterNewPassword: '请输入新密码（选填）',
@@ -601,7 +597,6 @@ export default {
         user: '用户',
         email: '邮箱',
         username: '用户名',
-        wechat: '微信号',
         notes: '备注',
         role: '角色',
         subscriptions: '订阅分组',
@@ -655,8 +650,6 @@ export default {
         emailPlaceholder: '请输入邮箱',
         usernameLabel: '用户名',
         usernamePlaceholder: '请输入用户名（选填）',
-        wechatLabel: '微信号',
-        wechatPlaceholder: '请输入微信号（选填）',
         notesLabel: '备注',
         notesPlaceholder: '请输入备注（仅管理员可见）',
         notesHint: '此备注仅对管理员可见',
@@ -711,7 +704,67 @@ export default {
       failedToDeposit: '充值失败',
       failedToWithdraw: '退款失败',
       useDepositWithdrawButtons: '请使用充值/退款按钮调整余额',
-      insufficientBalance: '余额不足，退款后余额不能为负数'
+      insufficientBalance: '余额不足，退款后余额不能为负数',
+      // Settings Dropdowns
+      filterSettings: '筛选设置',
+      columnSettings: '列设置',
+      filterValue: '输入值',
+      // User Attributes
+      attributes: {
+        title: '用户属性配置',
+        description: '配置用户的自定义属性字段',
+        configButton: '属性配置',
+        addAttribute: '添加属性',
+        editAttribute: '编辑属性',
+        deleteAttribute: '删除属性',
+        deleteConfirm: "确定要删除属性 '{name}' 吗？所有用户的该属性值将被删除。",
+        noAttributes: '暂无自定义属性',
+        noAttributesHint: '点击上方按钮添加自定义属性',
+        key: '属性键',
+        keyHint: '用于程序引用，只能包含字母、数字和下划线',
+        name: '显示名称',
+        nameHint: '在表单中显示的名称',
+        type: '属性类型',
+        fieldDescription: '描述',
+        fieldDescriptionHint: '属性的说明文字',
+        placeholder: '占位符',
+        placeholderHint: '输入框的提示文字',
+        required: '必填',
+        enabled: '启用',
+        options: '选项配置',
+        optionsHint: '用于单选/多选类型',
+        addOption: '添加选项',
+        optionValue: '选项值',
+        optionLabel: '显示文本',
+        validation: '验证规则',
+        minLength: '最小长度',
+        maxLength: '最大长度',
+        min: '最小值',
+        max: '最大值',
+        pattern: '正则表达式',
+        patternMessage: '验证失败提示',
+        types: {
+          text: '单行文本',
+          textarea: '多行文本',
+          number: '数字',
+          email: '邮箱',
+          url: '链接',
+          date: '日期',
+          select: '单选',
+          multi_select: '多选'
+        },
+        created: '属性创建成功',
+        updated: '属性更新成功',
+        deleted: '属性删除成功',
+        reordered: '属性排序更新成功',
+        failedToLoad: '加载属性列表失败',
+        failedToCreate: '创建属性失败',
+        failedToUpdate: '更新属性失败',
+        failedToDelete: '删除属性失败',
+        failedToReorder: '更新排序失败',
+        keyExists: '属性键已存在',
+        dragToReorder: '拖拽排序'
+      }
     },
 
     // Groups Management