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/docs/swagger.yaml

@@ -610,14 +610,32 @@ definitions:
     type: object
   httpapi.PricingEstimateResponse:
     properties:
+      candidateCount:
+        example: 2
+        type: integer
+      currency:
+        example: resource
+        type: string
       items:
         items:
           additionalProperties: true
           type: object
         type: array
-      resolver:
-        example: effective-pricing-v1
+      pricingVersion:
+        example: effective-pricing-v2
         type: string
+      requestFingerprint:
+        example: 76ef6a537de8e71bd1ca93acadc078dbdbfa9f17e45224e4f9df59f535d2886f
+        type: string
+      reservationAmount:
+        example: 2.75
+        type: number
+      resolver:
+        example: effective-pricing-v2
+        type: string
+      totalAmount:
+        example: 1.25
+        type: number
     type: object
   httpapi.PricingRuleListResponse:
     properties:
@@ -2485,11 +2503,17 @@ definitions:
       dynamicWeight:
         additionalProperties: {}
         type: object
+      effectiveFrom:
+        type: string
+      effectiveTo:
+        type: string
       formulaConfig:
         additionalProperties: {}
         type: object
       id:
         type: string
+      isFree:
+        type: boolean
       metadata:
         additionalProperties: {}
         type: object
@@ -2531,9 +2555,15 @@ definitions:
       dynamicWeight:
         additionalProperties: {}
         type: object
+      effectiveFrom:
+        type: string
+      effectiveTo:
+        type: string
       formulaConfig:
         additionalProperties: {}
         type: object
+      isFree:
+        type: boolean
       metadata:
         additionalProperties: {}
         type: object
@@ -6841,6 +6871,10 @@ paths:
           description: Internal Server Error
           schema:
             $ref: '#/definitions/httpapi.ErrorEnvelope'
+        "503":
+          description: Service Unavailable
+          schema:
+            $ref: '#/definitions/httpapi.ErrorEnvelope'
       security:
       - BearerAuth: []
       summary: 估算请求价格