GitLab

H5: diffSettings now tracks 5 balance/quota notify fields in audit log
M15: log.Printf audit log migrated to slog.Info, removed "log" import
M14: New frontend/src/constants/account.ts with shared constants
     QuotaNotifyToggle.vue uses QUOTA_THRESHOLD_TYPE_FIXED/PERCENTAGE
L2: UsageTable.vue uses BILLING_MODE_TOKEN/IMAGE from billingMode.ts

Threshold now represents remaining quota instead of usage amount:
- Fixed ($): threshold=400, limit=1000 → alert when remaining drops to $400
  (i.e., usage reaches $600)
- Percentage (%): threshold=30%, limit=1000 → alert when remaining drops
  to 30% (i.e., usage reaches $700)

Also:
- Rename 告警阈值 → 提醒阈值 in i18n
- Widen type dropdown to w-16 for proper $ / % display

- QuotaNotifyToggle: add $ or % suffix to threshold input based on type
- QuotaLimitCard: combine reset mode and notify toggle on same row
  to reduce vertical height for daily/weekly sections
- Remove redundant ml-4 indentation from QuotaNotifyToggle

- Add global toggle for account quota notification in admin settings
- Add percentage-based threshold type for per-account quota alerts
- Hide balance notify card on user profile when global toggle is off
- Expose balance_low_notify_enabled and account_quota_notify_enabled in PublicSettings
- Add threshold type (fixed/percentage) to QuotaNotifyToggle with $ / % switcher

- Fix accountCost calculation in finalizePostUsageBilling to match
  postUsageBilling (always multiply by AccountRateMultiplier)
- Use strings.EqualFold for email dedup in collectBalanceNotifyRecipients
- Extract CheckAccountQuotaAfterIncrement into smaller functions:
  buildQuotaDims + asyncSendQuotaAlert (< 30 lines each)
- Add "not splittable" comments for HTML template functions
- Extract QuotaNotifyToggle.vue sub-component to reduce
  QuotaLimitCard.vue from 404 to 339 lines