fix(billing): correct tiered billing settlement and edge cases

- quota.go: add missing SettleBilling call in PostWssConsumeQuota
- text_quota.go: gate InjectTieredBillingInfo on tieredBillingApplied bool
  instead of tieredResult != nil, so fallback billing still logs metadata
- price.go: remove quotaBeforeGroup == 0 from freeModel condition to avoid
  bypassing settlement for output-only expressions
- tiered_settle.go: split cc/cc1h subtraction using UsageSemantic to
  distinguish OpenAI vs Claude cache creation token formats
- pricing.go: only set BillingMode when a non-empty expression exists
- useModelPricingEditorState.js: only write billing_mode when
  finalBillingExpr is non-empty

relay/helper/price.go

@@ -269,7 +269,7 @@ func modelPriceHelperTiered(c *gin.Context, info *relaycommon.RelayInfo, promptT
 
 	freeModel := false
 	if !operation_setting.GetQuotaSetting().EnableFreeModelPreConsume {
-		if groupRatioInfo.GroupRatio == 0 || quotaBeforeGroup == 0 {
+		if groupRatioInfo.GroupRatio == 0 {
 			preConsumedQuota = 0
 			freeModel = true
 		}