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

service/quota.go

@@ -226,6 +226,10 @@ func PostWssConsumeQuota(ctx *gin.Context, relayInfo *relaycommon.RelayInfo, mod
 		model.UpdateChannelUsedQuota(relayInfo.ChannelId, quota)
 	}
 
+	if err := SettleBilling(ctx, relayInfo, quota); err != nil {
+		logger.LogError(ctx, "error settling billing: "+err.Error())
+	}
+
 	logModel := modelName
 	if extraContent != "" {
 		logContent += ", " + extraContent