feat(channel): 渠道管理全链路集成 — 模型映射、定价、限制、用量统计

- 渠道模型映射：支持精确匹配和通配符映射，按平台隔离
- 渠道模型定价：支持 token/按次/图片三种计费模式，区间分层定价
- 模型限制：渠道可限制仅允许定价列表中的模型
- 计费模型来源：支持 requested/upstream 两种计费模型选择
- 用量统计：usage_logs 新增 channel_id/model_mapping_chain/billing_tier/billing_mode 字段
- Dashboard 支持 model_source 维度（requested/upstream/mapping）查看模型统计
- 全部 gateway handler 统一接入 ResolveChannelMappingAndRestrict
- 修复测试：同步 SoraGenerationRepository 接口、SQL INSERT 参数、scan 字段

backend/internal/handler/admin/dashboard_handler.go

@@ -636,6 +636,40 @@ func (h *DashboardHandler) GetUserBreakdown(c *gin.Context) {
 	dim.Endpoint = c.Query("endpoint")
 	dim.EndpointType = c.DefaultQuery("endpoint_type", "inbound")
 
+	// Additional filter conditions
+	if v := c.Query("user_id"); v != "" {
+		if id, err := strconv.ParseInt(v, 10, 64); err == nil {
+			dim.UserID = id
+		}
+	}
+	if v := c.Query("api_key_id"); v != "" {
+		if id, err := strconv.ParseInt(v, 10, 64); err == nil {
+			dim.APIKeyID = id
+		}
+	}
+	if v := c.Query("account_id"); v != "" {
+		if id, err := strconv.ParseInt(v, 10, 64); err == nil {
+			dim.AccountID = id
+		}
+	}
+	if v := c.Query("request_type"); v != "" {
+		if rt, err := strconv.ParseInt(v, 10, 16); err == nil {
+			rtVal := int16(rt)
+			dim.RequestType = &rtVal
+		}
+	}
+	if v := c.Query("stream"); v != "" {
+		if s, err := strconv.ParseBool(v); err == nil {
+			dim.Stream = &s
+		}
+	}
+	if v := c.Query("billing_type"); v != "" {
+		if bt, err := strconv.ParseInt(v, 10, 8); err == nil {
+			btVal := int8(bt)
+			dim.BillingType = &btVal
+		}
+	}
+
 	limit := 50
 	if v := c.Query("limit"); v != "" {
 		if n, err := strconv.Atoi(v); err == nil && n > 0 && n <= 200 {