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).

model/task.go

@@ -100,9 +100,19 @@ type TaskPrivateData struct {
 	UpstreamTaskID string `json:"upstream_task_id,omitempty"` // 上游真实 task ID
 	ResultURL      string `json:"result_url,omitempty"`       // 任务成功后的结果 URL（视频地址等）
 	// 计费上下文：用于异步退款/差额结算（轮询阶段读取）
-	BillingSource  string `json:"billing_source,omitempty"`  // "wallet" 或 "subscription"
-	SubscriptionId int    `json:"subscription_id,omitempty"` // 订阅 ID，用于订阅退款
-	TokenId        int    `json:"token_id,omitempty"`        // 令牌 ID，用于令牌额度退款
+	BillingSource  string              `json:"billing_source,omitempty"`  // "wallet" 或 "subscription"
+	SubscriptionId int                 `json:"subscription_id,omitempty"` // 订阅 ID，用于订阅退款
+	TokenId        int                 `json:"token_id,omitempty"`        // 令牌 ID，用于令牌额度退款
+	BillingContext *TaskBillingContext `json:"billing_context,omitempty"` // 计费参数快照（用于轮询阶段重新计算）
+}
+
+// TaskBillingContext 记录任务提交时的计费参数，以便轮询阶段可以重新计算额度。
+type TaskBillingContext struct {
+	ModelPrice  float64            `json:"model_price,omitempty"`  // 模型单价
+	GroupRatio  float64            `json:"group_ratio,omitempty"`  // 分组倍率
+	ModelRatio  float64            `json:"model_ratio,omitempty"`  // 模型倍率
+	OtherRatios map[string]float64 `json:"other_ratios,omitempty"` // 附加倍率（时长、分辨率等）
+	ModelName   string             `json:"model_name,omitempty"`   // 模型名称
 }
 
 // GetUpstreamTaskID 获取上游真实 task ID（用于与 provider 通信）