fix(fee): default service fee to 0 when setting is empty

Read fee_service_charge_percentage only; no implicit 0.01 fallback.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/utils/serviceFee.ts

@@ -1,7 +1,7 @@
 import { ref } from 'vue'
 import { useSettingsStore } from '@/store/settingsStore'
 
-export const serviceFeePercentage = ref<number>(0.01)
+export const serviceFeePercentage = ref<number>(0)
 
 /**
  * @deprecated منطق کارمزد دیگر به این کلید وابسته نیست.
@@ -78,7 +78,8 @@ export async function loadServiceFeeFromSettings() {
         (s) => s?.key === 'fee_service_charge_percentage' && s?.is_active === true
       )
       if (feeSetting?.value !== undefined && feeSetting?.value !== null) {
-        serviceFeePercentage.value = Number(feeSetting.value)
+        const raw = String(feeSetting.value).trim()
+        serviceFeePercentage.value = raw === '' ? 0 : Number(raw)
       }
 
       const feeModeSetting = settings.find(