feat(task): add adaptor billing interface and async settlement framework

Add three billing lifecycle methods to the TaskAdaptor interface:
- EstimateBilling: compute OtherRatios from user request before pricing
- AdjustBillingOnSubmit: adjust ratios from upstream submit response
- AdjustBillingOnComplete: determine final quota at task terminal state

Introduce BaseBilling as embeddable no-op default for adaptors without
custom billing. Move Sora/Ali OtherRatios logic from shared validation
into per-adaptor EstimateBilling implementations.

Add TaskBillingContext to persist pricing params (model_price, group_ratio,
other_ratios) in task private data for async polling settlement.

Extract RecalculateTaskQuota as a general-purpose delta settlement
function and unify polling billing via settleTaskBillingOnComplete
(adaptor-first, then token-based fallback).

controller/relay.go

@@ -509,6 +509,13 @@ func RelayTask(c *gin.Context) {
 		task.PrivateData.BillingSource = relayInfo.BillingSource
 		task.PrivateData.SubscriptionId = relayInfo.SubscriptionId
 		task.PrivateData.TokenId = relayInfo.TokenId
+		task.PrivateData.BillingContext = &model.TaskBillingContext{
+			ModelPrice:  relayInfo.PriceData.ModelPrice,
+			GroupRatio:  relayInfo.PriceData.GroupRatioInfo.GroupRatio,
+			ModelRatio:  relayInfo.PriceData.ModelRatio,
+			OtherRatios: relayInfo.PriceData.OtherRatios,
+			ModelName:   result.ModelName,
+		}
 		task.Quota = result.Quota
 		task.Data = result.TaskData
 		task.Action = relayInfo.Action