feat(billing): 统一计价与候选冻结估算

新增 effective-pricing-v2、9 位十进制定点计算、显式免费校验和结构化缺价错误。估价与生产预处理覆盖全部可用候选，并按最大候选费用冻结；规则优先级为平台模型、平台、基准模型。\n\n同步计价契约和 OpenAPI，补充 Token 参数别名、视频五秒向上取整及缺价回归测试。\n\n验证：go test ./...、pnpm openapi、Web 测试与构建通过。

apps/api/internal/runner/pricing.go

@@ -11,10 +11,14 @@ import (
 )
 
 type EstimateResult struct {
-	Items       []any   `json:"items"`
-	Resolver    string  `json:"resolver"`
-	TotalAmount float64 `json:"totalAmount"`
-	Currency    string  `json:"currency"`
+	Items              []any   `json:"items"`
+	Resolver           string  `json:"resolver"`
+	TotalAmount        float64 `json:"totalAmount"`
+	ReservationAmount  float64 `json:"reservationAmount"`
+	Currency           string  `json:"currency"`
+	CandidateCount     int     `json:"candidateCount"`
+	PricingVersion     string  `json:"pricingVersion"`
+	RequestFingerprint string  `json:"requestFingerprint"`
 }
 
 func (s *Service) Estimate(ctx context.Context, kind string, model string, body map[string]any, user *auth.User) (EstimateResult, error) {
@@ -32,15 +36,21 @@ func (s *Service) Estimate(ctx context.Context, kind string, model string, body
 	if err != nil {
 		return EstimateResult{}, err
 	}
-	candidate := candidates[0]
-	body = preprocessRequest(kind, body, candidate)
-	items := s.estimatedBillings(ctx, user, kind, body, candidate)
-	return EstimateResult{
-		Items:       items,
-		Resolver:    "effective-pricing-v1",
-		TotalAmount: totalBillingAmount(items),
-		Currency:    billingCurrency(items),
-	}, nil
+	estimates := make([]candidateEstimate, 0, len(candidates))
+	var pricingErr error
+	for _, candidate := range candidates {
+		candidateBody := preprocessRequest(kind, cloneMap(body), candidate)
+		estimate, candidateErr := s.estimateCandidateV2(ctx, user, kind, candidateBody, candidate)
+		if candidateErr != nil {
+			pricingErr = candidateErr
+			continue
+		}
+		estimates = append(estimates, estimate)
+	}
+	if len(estimates) == 0 && pricingErr != nil {
+		return EstimateResult{}, pricingErr
+	}
+	return buildEstimateResult(estimates, pricingRequestFingerprint(kind, model, body))
 }
 
 func (s *Service) estimatedBillings(ctx context.Context, user *auth.User, kind string, body map[string]any, candidate store.RuntimeModelCandidate) []any {