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/api/admin/affiliates.ts

@@ -0,0 +1,108 @@
+/**
+ * Admin Affiliate API endpoints
+ * Manage per-user affiliate (邀请返利) configurations:
+ * exclusive invite codes (overrides aff_code) and exclusive rebate rates.
+ */
+
+import { apiClient } from '../client'
+import type { PaginatedResponse } from '@/types'
+
+export interface AffiliateAdminEntry {
+  user_id: number
+  email: string
+  username: string
+  aff_code: string
+  aff_code_custom: boolean
+  aff_rebate_rate_percent?: number | null
+  aff_count: number
+}
+
+export interface ListAffiliateUsersParams {
+  page?: number
+  page_size?: number
+  search?: string
+}
+
+export interface UpdateAffiliateUserRequest {
+  aff_code?: string
+  aff_rebate_rate_percent?: number | null
+  /** Set true to explicitly clear the per-user rate (sets it to NULL). */
+  clear_rebate_rate?: boolean
+}
+
+export interface BatchSetRateRequest {
+  user_ids: number[]
+  aff_rebate_rate_percent?: number | null
+  /** Set true to clear rates instead of setting. */
+  clear?: boolean
+}
+
+export interface SimpleUser {
+  id: number
+  email: string
+  username: string
+}
+
+export async function listUsers(
+  params: ListAffiliateUsersParams = {},
+): Promise<PaginatedResponse<AffiliateAdminEntry>> {
+  const { data } = await apiClient.get<PaginatedResponse<AffiliateAdminEntry>>(
+    '/admin/affiliates/users',
+    {
+      params: {
+        page: params.page ?? 1,
+        page_size: params.page_size ?? 20,
+        search: params.search ?? '',
+      },
+    },
+  )
+  return data
+}
+
+export async function lookupUsers(q: string): Promise<SimpleUser[]> {
+  const { data } = await apiClient.get<SimpleUser[]>(
+    '/admin/affiliates/users/lookup',
+    { params: { q } },
+  )
+  return data
+}
+
+export async function updateUserSettings(
+  userId: number,
+  payload: UpdateAffiliateUserRequest,
+): Promise<{ user_id: number }> {
+  const { data } = await apiClient.put<{ user_id: number }>(
+    `/admin/affiliates/users/${userId}`,
+    payload,
+  )
+  return data
+}
+
+export async function clearUserSettings(
+  userId: number,
+): Promise<{ user_id: number }> {
+  const { data } = await apiClient.delete<{ user_id: number }>(
+    `/admin/affiliates/users/${userId}`,
+  )
+  return data
+}
+
+export async function batchSetRate(
+  payload: BatchSetRateRequest,
+): Promise<{ affected: number }> {
+  const { data } = await apiClient.post<{ affected: number }>(
+    '/admin/affiliates/users/batch-rate',
+    payload,
+  )
+  return data
+}
+
+export const affiliatesAPI = {
+  listUsers,
+  lookupUsers,
+  updateUserSettings,
+  clearUserSettings,
+  batchSetRate,
+}
+
+export default affiliatesAPI