feat(affiliate): add feature toggle and per-user custom invite settings

- 在系统设置「功能开关」中新增邀请返利总开关，默认关闭；
  关闭态：菜单隐藏、注册忽略 aff、新充值不返利，但已有 quota 仍可转余额
- 支持管理员为指定用户设置专属邀请码（覆盖随机码，全局唯一）
- 支持管理员为指定用户设置专属返利比例（覆盖全局比例，可单条/批量调整）
- 在系统设置邀请返利卡片内嵌入专属用户管理表格（搜索/编辑/批量/删除），
  删除采用项目通用 ConfirmDialog，会同时清除专属比例并把邀请码重置为系统随机码
- /affiliate 用户页新增「我的返利比例」卡片与动态使用说明，让用户直观看到
  分享后能拿到多少（同源 resolveRebateRatePercent 计算，与实际充值一致）
- 新增数据库迁移 132 添加 aff_rebate_rate_percent 与 aff_code_custom 列
- 新增 admin 路由组 /api/v1/admin/affiliates/users/* 共 5 个端点
- AffiliateService 改为只依赖 *SettingService，去除冗余的 SettingRepository
- 邀请码格式校验放宽到 [A-Z0-9_-]{4,32}，兼容旧 12 位系统码与新自定义码
- 补充单元测试与集成测试覆盖新方法、冲突路径与边界值

frontend/src/i18n/locales/en.ts

@@ -985,6 +985,8 @@ export default {
     loadFailed: 'Failed to load affiliate data',
     transferFailed: 'Failed to transfer affiliate quota',
     stats: {
+      rebateRate: 'My Rebate Rate',
+      rebateRateHint: 'What you earn each time an invitee recharges',
       invitedUsers: 'Invited Users',
       availableQuota: 'Available Rebate Quota',
       totalQuota: 'Historical Rebate Quota'
@@ -1009,7 +1011,7 @@ export default {
     tips: {
       title: 'How It Works',
       line1: 'Share your affiliate code or invite link with new users.',
-      line2: 'When invitees recharge, you receive rebate quota based on the configured rate.',
+      line2: 'When invitees recharge, you receive {rate} of the recharge as rebate quota.',
       line3: 'Transfer rebate quota to balance at any time.'
     }
   },
@@ -4779,6 +4781,55 @@ export default {
           enabled: 'Enable Available Channels',
           enabledHint: 'When off, the sidebar entry is hidden and the endpoint returns an empty list.',
         },
+        affiliate: {
+          title: 'Affiliate (Invite Rebate)',
+          description: 'Existing users invite new ones; the inviter earns a percentage rebate on the invitee’s recharges. Disabled by default.',
+          enabled: 'Enable Affiliate',
+          enabledHint: 'When off, the affiliate menu is hidden, the aff parameter is ignored at signup, and new recharges generate no rebate. Existing rebate balances can still be transferred.',
+          rebateRate: 'Global Rebate Rate',
+          rebateRateHint: 'Default percentage given back to the inviter on recharges (0-100, e.g. 10 = 10%).',
+          customUsers: {
+            title: 'Per-User Overrides',
+            description: 'Set a custom invite code or exclusive rebate rate for specific users. Lists only users that have an override applied.',
+            addButton: 'Add Custom User',
+            searchPlaceholder: 'Search by email or username',
+            batchButton: 'Batch Set Rate ({count} selected)',
+            empty: 'No users with custom affiliate settings yet',
+            customBadge: 'custom',
+            useGlobal: 'use global',
+            resetTitle: 'Reset Custom Settings',
+            resetMessage: 'Reset all custom settings for {email}?\n• The exclusive rebate rate will be cleared (fall back to the global rate)\n• The invite code will be regenerated as a new system code (previously shared links will stop working)',
+            totalLabel: '{total} total',
+            col: {
+              email: 'Email',
+              username: 'Username',
+              code: 'Invite Code',
+              rate: 'Custom Rate',
+              actions: 'Actions',
+            },
+          },
+          modal: {
+            addTitle: 'Add Custom User',
+            editTitle: 'Edit Custom Settings',
+            userLabel: 'User',
+            userPlaceholder: 'Search by email or username',
+            changeUser: 'Change user',
+            codeLabel: 'Custom Invite Code (optional)',
+            codePlaceholder: 'e.g. VIP2026',
+            codeHint: '4-32 characters; A-Z, 0-9, underscore, dash. Leave empty to keep current. Input is upper-cased.',
+            rateLabel: 'Exclusive Rebate Rate (optional)',
+            ratePlaceholder: 'e.g. 30',
+            rateHint: '0-100. Leave empty (in edit mode) to clear and fall back to the global rate.',
+            errorBadRate: 'Please enter a number between 0 and 100',
+            errorEmpty: 'Fill at least one: custom invite code or exclusive rebate rate',
+          },
+          batchModal: {
+            title: 'Batch Set Rate ({count} users selected)',
+            hint: 'Apply the same exclusive rebate rate to all selected users.',
+            placeholder: 'e.g. 30',
+            clearHint: 'Submitting empty will clear the exclusive rate for selected users.',
+          },
+        },
       },
       emailTabDisabledTitle: 'Email Verification Not Enabled',
       emailTabDisabledHint: 'Enable email verification in the Security tab to configure SMTP settings.',

frontend/src/i18n/locales/zh.ts

@@ -989,6 +989,8 @@ export default {
     loadFailed: '加载邀请返利数据失败',
     transferFailed: '转入余额失败',
     stats: {
+      rebateRate: '我的返利比例',
+      rebateRateHint: '被邀请用户每次充值后你可获得的返利比例',
       invitedUsers: '邀请人数',
       availableQuota: '可转返利额度',
       totalQuota: '历史返利额度'
@@ -1013,7 +1015,7 @@ export default {
     tips: {
       title: '使用说明',
       line1: '将邀请码或邀请链接分享给新用户。',
-      line2: '被邀请用户充值后，你可获得对应比例的返利额度。',
+      line2: '被邀请用户充值后，你可获得 {rate} 的返利额度。',
       line3: '返利额度可随时转入账户余额。'
     }
   },
@@ -4942,6 +4944,55 @@ export default {
           enabled: '启用可用渠道',
           enabledHint: '关闭后用户端侧边栏入口隐藏，接口返回空数组。',
         },
+        affiliate: {
+          title: '邀请返利',
+          description: '老用户邀请新用户注册，新用户充值后老用户按比例获得返利额度。默认关闭。',
+          enabled: '启用邀请返利',
+          enabledHint: '关闭后用户菜单中的邀请页面入口隐藏、注册时忽略邀请码、新充值不再产生返利。已有返利额度仍可转入余额。',
+          rebateRate: '全局返利比例',
+          rebateRateHint: '充值后返给邀请人的默认比例（0-100%，例如填写 10 表示返利 10%）。',
+          customUsers: {
+            title: '专属用户配置',
+            description: '为指定用户设置专属邀请码或专属返利比例。仅展示已设置过专属配置的用户。',
+            addButton: '添加专属用户',
+            searchPlaceholder: '搜索邮箱或用户名',
+            batchButton: '批量设置比例（已选 {count}）',
+            empty: '暂无专属配置用户',
+            customBadge: '自定义',
+            useGlobal: '沿用全局',
+            resetTitle: '重置该用户的专属配置',
+            resetMessage: '确认将 {email} 的专属配置全部重置为默认？\n• 专属返利比例将清除（沿用全局）\n• 邀请码将重新生成为系统随机码（已分发的旧邀请链接将失效）',
+            totalLabel: '共 {total} 条',
+            col: {
+              email: '邮箱',
+              username: '用户名',
+              code: '邀请码',
+              rate: '专属比例',
+              actions: '操作',
+            },
+          },
+          modal: {
+            addTitle: '添加专属用户',
+            editTitle: '编辑专属配置',
+            userLabel: '用户',
+            userPlaceholder: '搜索邮箱或用户名',
+            changeUser: '更换用户',
+            codeLabel: '专属邀请码（可选）',
+            codePlaceholder: '例如 VIP2026',
+            codeHint: '4-32 位，仅支持大写字母、数字、下划线、连字符；留空表示不修改；输入将自动转大写。',
+            rateLabel: '专属返利比例（可选）',
+            ratePlaceholder: '例如 30',
+            rateHint: '0-100%；留空（编辑模式下）表示清除专属比例并沿用全局。',
+            errorBadRate: '请输入 0-100 之间的比例',
+            errorEmpty: '至少填写一项：专属邀请码或专属返利比例',
+          },
+          batchModal: {
+            title: '批量设置专属比例（已选 {count} 个用户）',
+            hint: '为所选用户统一设置专属返利比例。',
+            placeholder: '例如 30',
+            clearHint: '留空提交将清除所选用户的专属比例。',
+          },
+        },
       },
       emailTabDisabledTitle: '邮箱验证未启用',
       emailTabDisabledHint: '请在「安全与认证」选项卡中启用邮箱验证后，再配置 SMTP 设置。',