fix: 按数量计价模式无需填写接单金额

选择按数量×单价时，接单金额可留空（建单时按 单价×SKU文字数量 计算总价）；
仅当接单金额和单价都为空时才拦截

apps/backend/src/services/worker-platform/admin-service.ts

@@ -217,6 +217,10 @@ export async function saveAdminWorkProductRule(payload: JsonObject = {}) {
   }
 
   const rewardAmount = normalizeAmountFen(payload.rewardAmount ?? payload.rewardAmountYuan, 0)
+  const unitPriceFen =
+    payload.unitPrice === undefined && payload.unitPriceYuan === undefined
+      ? 0
+      : normalizeAmountFen(payload.unitPrice ?? payload.unitPriceYuan, 0)
   const sharingEnabled = normalizeBoolean(
     payload.sharingEnabled ?? payload.sharing_enabled,
     false,
@@ -243,7 +247,7 @@ export async function saveAdminWorkProductRule(payload: JsonObject = {}) {
         errorCode: 'work_product_rule_sharing_amount_invalid',
       })
     }
-  } else if (rewardAmount <= 0) {
+  } else if (rewardAmount <= 0 && unitPriceFen <= 0) {
     throw createHttpError('接单金额必须大于 0', {
       statusCode: 400,
       errorCode: 'work_product_rule_reward_invalid',
@@ -288,10 +292,7 @@ export async function saveAdminWorkProductRule(payload: JsonObject = {}) {
     enabled: normalizeBoolean(payload.enabled, true),
     autoCreate: normalizeBoolean(payload.autoCreate ?? payload.auto_create, false),
     rewardAmount: finalRewardAmount,
-    unitPriceFen:
-      payload.unitPrice === undefined && payload.unitPriceYuan === undefined
-        ? 0
-        : normalizeAmountFen(payload.unitPrice ?? payload.unitPriceYuan, 0),
+    unitPriceFen,
     requiredDepositAmount,
     depositThresholdAmount,
     sharingEnabled,