feat(tenant): per-tenant brand and question limit overrides

Add nullable brand_limit / question_limit columns on tenants so ops
admins can override the plan-derived brand-library quotas per account.
When set, these take precedence over config.yml plan defaults across the
brand-library summary, question materialization, and the daily
monitoring worker's primary-client plan resolution.

Ops side exposes them on admin-user create plus a new
PUT /admin-users/:id/limits endpoint, invalidating the brand-library
summary cache on change. The ops-web AdminUsers view gains matching
inputs on the create and edit modals.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/shared/swagger/descriptions.go

@@ -38,6 +38,7 @@ var routeDocs = map[string]routeDoc{
 	"POST /api/ops/admin-users":                         {"新建租户管理员", "创建租户管理员账号。"},
 	"GET /api/ops/admin-users/:id":                      {"租户管理员详情", "读取租户管理员账号详情。"},
 	"PATCH /api/ops/admin-users/:id":                    {"更新租户管理员", "更新租户管理员基础资料。"},
+	"PUT /api/ops/admin-users/:id/limits":               {"调整品牌库限额", "设置租户管理员账号的品牌和问题数量覆盖限额。"},
 	"POST /api/ops/admin-users/:id/plan":                {"调整租户套餐", "调整租户管理员账号绑定的套餐。"},
 	"POST /api/ops/admin-users/:id/subscription-expiry": {"调整订阅到期时间", "更新租户管理员账号订阅到期时间。"},
 	"POST /api/ops/admin-users/:id/reset-plan-usage":    {"重置套餐用量", "重置租户管理员账号套餐用量。"},