Merge origin/main into feat/channel-monitor-v2-ops-ui

Resolves three conflicts, all of the "both branches appended to the same
block" shape. Every one is resolved as a union of both sides; nothing from
either parent is dropped.

- handler/admin/setting_handler_update.go: keep ChannelMonitorHideThroughput
  (V2) alongside GrokDefaultTextModel / GrokCrossClientModelMapEnabled /
  GrokDefaultBaseURLMode (#5408). UpdateSettings writes every key on each
  save, so dropping either side would reset those settings to zero values.
- service/domain_constants.go: keep SettingKeyChannelMonitorHideThroughput
  and the three SettingKeyGrok* constants.
- repository/migrations_runner.go: keep the 195 checksum rule (V2) and the
  218/219/220 rules (#5408).

frontend/src/views/user/UsageView.vue

@@ -231,7 +231,7 @@ import Icon from '@/components/icons/Icon.vue'
 import UserErrorRequestsTable from '@/components/user/UserErrorRequestsTable.vue'
 import { getPersistedPageSize } from '@/composables/usePersistedPageSize'
 import { formatReasoningEffort } from '@/utils/format'
-import { BILLING_MODE_IMAGE, getBillingModeLabel } from '@/utils/billingMode'
+import { getBillingModeLabel, getDisplayBillingMode as resolveDisplayBillingMode } from '@/utils/billingMode'
 import { resolveUsageRequestType, requestTypeToLegacyStream } from '@/utils/usageRequestType'
 import type {
   ApiKey,
@@ -605,10 +605,7 @@ const getRequestTypeExportText = (log: UsageLog): string => {
 
 const getDisplayBillingMode = (
   row: Pick<UsageLog, 'billing_mode' | 'image_count'> | null | undefined
-): string | null | undefined => {
-  if ((row?.image_count ?? 0) > 0) return BILLING_MODE_IMAGE
-  return row?.billing_mode
-}
+): string | null | undefined => resolveDisplayBillingMode(row)
 
 const escapeCSVValue = (value: unknown): string => {
   if (value == null) return ''