feat(distribution): 支持分站发布群固定二维码

主站分销配置可为每个站点绑定可复用企微码，号主在该站上传账号后发到对应发布群，不再消耗主站码池。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/modules/distribution/dto.go

@@ -15,6 +15,7 @@ type SiteDTO struct {
 	AnnouncementsJSON     string    `json:"announcements_json"`
 	FooterInfoJSON        string    `json:"footer_info_json"`
 	DefaultSupportGroupID *uint64   `json:"default_support_group_id,omitempty"`
+	ListingQrcodeURL      string    `json:"listing_qrcode_url"`
 	TaxEnabled            bool      `json:"tax_enabled"`
 	TaxRateBPS            int64     `json:"tax_rate_bps"`
 	SettlementHoldDays    int       `json:"settlement_hold_days"`
@@ -28,6 +29,7 @@ type CreateSiteRequest struct {
 	Domain                string  `json:"domain" binding:"required,max=255"`
 	DisplayAccountEnabled *bool   `json:"display_account_enabled"`
 	DefaultSupportGroupID *uint64 `json:"default_support_group_id"`
+	ListingQrcodeURL      *string `json:"listing_qrcode_url"`
 	TaxEnabled            *bool   `json:"tax_enabled"`
 	TaxRateBPS            *int64  `json:"tax_rate_bps"`
 	SettlementHoldDays    *int    `json:"settlement_hold_days"`
@@ -39,6 +41,7 @@ type UpdateSiteRequest struct {
 	Status                *string `json:"status"`
 	DisplayAccountEnabled *bool   `json:"display_account_enabled"`
 	DefaultSupportGroupID *uint64 `json:"default_support_group_id"`
+	ListingQrcodeURL      *string `json:"listing_qrcode_url"`
 	TaxEnabled            *bool   `json:"tax_enabled"`
 	TaxRateBPS            *int64  `json:"tax_rate_bps"`
 	SettlementHoldDays    *int    `json:"settlement_hold_days"`