GitLab

- Security: force token_uri to Google default, preventing SSRF via crafted service account JSON
- Dedup: extract shared getVertexServiceAccountAccessToken() to eliminate ~35 lines of duplication between ClaudeTokenProvider and GeminiTokenProvider
- Fix: apply model mapping + Vertex model ID normalization in forward_as_responses and forward_as_chat_completions paths
- Fix: exclude service_account from AI Studio endpoint selection (Vertex cannot serve generativelanguage.googleapis.com)
- Feature: add model restriction/mapping UI for service_account in EditAccountModal
- Dedup: extract VERTEX_LOCATION_OPTIONS to shared constants
- i18n: replace all hardcoded Chinese strings in Vertex UI with translation keys

Security (HIGH):
- Normalize all Redis cache keys to lowercase (verifyCode, passwordReset)
- Fix verify code TTL renewal on failed attempts: use remaining TTL via
  ExpiresAt field instead of resetting to full 15-minute window
- Add 3 missing fields to diffSettings audit log (promo_code, invitation_code,
  custom_endpoints)

Code quality (MEDIUM):
- Extract filterVerifiedEmails shared helper (balance_notify_service.go)
- Add Pricing array non-empty validation for channel pricing rules
- Add platform token semantics comment in gateway_service.go
- Complete validatePlanPatch test coverage (+10 test cases)
- Replace string types with QuotaThresholdType/QuotaResetMode across frontend
- Remove duplicate getPlatformTextColor/getRateBadgeClass in ChannelsView
- Return EMAIL_NOT_FOUND error on RemoveNotifyEmail miss

UI improvements:
- Reorder cost tooltip: user billing above separator, account billing below
- Add NaN guard to accountBilled function
- Move timezone selector inline into reset-mode row (no longer standalone)

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