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。

packages/contracts/src/index.ts

@@ -184,6 +184,7 @@ export interface PricingRule {
     | string;
   unit: '1k_tokens' | 'image' | '5s' | 'second' | 'character_1k' | 'item' | string;
   basePrice: number;
+  isFree: boolean;
   currency: 'resource' | 'credit' | 'cny' | 'usd' | string;
   baseWeight?: Record<string, unknown>;
   dynamicWeight?: Record<string, unknown>;
@@ -193,6 +194,8 @@ export interface PricingRule {
   priority: number;
   status: 'active' | 'deprecated' | 'hidden' | string;
   metadata?: Record<string, unknown>;
+  effectiveFrom?: string;
+  effectiveTo?: string;
   createdAt: string;
   updatedAt: string;
 }
@@ -203,6 +206,7 @@ export interface PricingRuleInput {
   resourceType: string;
   unit: string;
   basePrice: number;
+  isFree?: boolean;
   currency?: string;
   baseWeight?: Record<string, unknown>;
   dynamicWeight?: Record<string, unknown>;
@@ -212,6 +216,8 @@ export interface PricingRuleInput {
   priority?: number;
   status?: 'active' | 'deprecated' | 'hidden' | string;
   metadata?: Record<string, unknown>;
+  effectiveFrom?: string;
+  effectiveTo?: string;
 }
 
 export interface PricingRuleSet {
@@ -548,7 +554,11 @@ export interface GatewayPricingEstimate {
   items: GatewayPricingEstimateItem[];
   resolver: string;
   totalAmount?: number;
+  reservationAmount?: number;
   currency?: string;
+  candidateCount: number;
+  pricingVersion: string;
+  requestFingerprint: string;
 }
 
 export interface GatewayWalletAccount {