GitLab

- backend: 删除 gpt-5 / 5.1 / 5.1-codex / 5.1-codex-max / 5.1-codex-mini / 5.2-codex / 5.4-nano 的内置映射与 DefaultModels 条目
- backend: normalizeCodexModel 默认兜底由 gpt-5.1 改为 gpt-5.4，gpt-5.3-codex-spark 独立保留映射
- backend: 修复 isOpenAIGPT54Model 与 shouldAutoInjectPromptCacheKeyForCompat 对 claude / gpt-4o 的误判（之前依赖 gpt-5.1 作为非 GPT 族的隐式 sentinel，改后需要显式前缀守卫）
- backend: 清理 billing_service 中已不可达的 fallback 价格与 switch 分支
- frontend: 从白名单、OpenCode 配置、预设映射中移除已下线模型
- 同步更新所有相关单测

Refs: #1758, parallels upstream #1759 but adds downstream guard fixes

Pairs with the backend structured payment errors (reason + metadata). The
frontend now maps reason codes to localized messages with metadata as
interpolation variables, and automatically localizes raw config-field names
(e.g. "certSerial" → "证书序列号") using the existing UI-label i18n
namespace.

- frontend/src/utils/apiError.ts
  - extractApiErrorCode now prefers the string `reason` over the numeric HTTP
    `code`; reason is granular enough to drive i18n lookup, HTTP code is not.
  - New extractApiErrorMetadata to pull interpolation params off the error.
  - New extractI18nErrorMessage(err, t, namespace, fallback): looks up
    `<namespace>.<REASON>` in i18n and substitutes metadata. Before
    substitution, `metadata.key` and `metadata.keys` (slash-joined) are
    re-translated through `admin.settings.payment.field_<key>` so users see
    "缺少必填项：证书序列号" instead of "缺少必填项：certSerial".

- frontend/src/i18n/locales/{zh,en}.ts
  - Add payment.errors entries for every structured reason code returned by
    the backend (PAYMENT_DISABLED, INVALID_AMOUNT, TOO_MANY_PENDING,
    DAILY_LIMIT_EXCEEDED, NO_AVAILABLE_INSTANCE, PAYMENT_PROVIDER_MISCONFIGURED,
    WXPAY_CONFIG_MISSING_KEY / INVALID_KEY_LENGTH / INVALID_KEY, NOT_FOUND,
    FORBIDDEN, CONFLICT, INVALID_ORDER_TYPE, INVALID_STATUS,
    BALANCE_NOT_ENOUGH, REFUND_AMOUNT_EXCEEDED, REFUND_FAILED, and more),
    with placeholders for template variables.

- 13 payment-related Vue files
  - Migrate catch-block error reporting from extractApiErrorMessage to
    extractI18nErrorMessage(err, t, 'payment.errors', fallback).
  - Remove the ad-hoc paymentErrorMap computed in SettingsView.vue, which the
    new helper supersedes (it reads i18n directly via t).

- frontend/src/components/payment/providerConfig.ts
  - wxpay: publicKey and publicKeyId are now required (was optional), matching
    the pubkey-only verifier direction; certSerial is already required.

This PR is drop-in safe: reason-preferring extractApiErrorCode is backward
compatible with callers that pass their own i18nMap, and error codes missing
from i18n fall back to the existing message-based path.

Add quota exceeded check to IsSchedulable() and refactor
shouldClearStickySession to delegate to IsSchedulable(), eliminating
duplicated logic and fixing missed overload/rate-limit/expired checks.
Frontend displays quota exceeded status independently via quota fields.