feat(rectifier): 请求整流器增加 API Key 账号签名整流支持

新增独立开关控制 API Key 账号的签名整流功能，支持配置自定义
匹配关键词以捕获不同格式的上游错误响应。

- 新增 apikey_signature_enabled 开关（默认关闭）
- 新增 apikey_signature_patterns 自定义关键词配置
- 内置签名检测规则对 API Key 账号同样生效
- 自定义关键词对完整响应体做不区分大小写匹配
- 重试二阶段检测仅做模式匹配，不重复校验开关
- Handler 层校验关键词数量（≤50）和长度（≤500）
- API 响应 nil patterns 统一序列化为空数组
- OAuth/SetupToken/Upstream/Bedrock 账号行为不变

frontend/src/i18n/locales/en.ts

@@ -4473,6 +4473,14 @@ export default {
         thinkingSignatureHint: 'Automatically strip signatures and retry when upstream returns thinking block signature validation errors',
         thinkingBudget: 'Thinking Budget Rectifier',
         thinkingBudgetHint: 'Automatically set budget to 32000 and retry when upstream returns budget_tokens constraint error (≥1024)',
+        apikeySignature: 'API Key Signature Rectifier',
+        apikeySignatureHint:
+          'Automatically strip signatures and retry when API Key accounts receive signature-related errors (built-in patterns always apply)',
+        apikeyPatterns: 'Custom Match Patterns',
+        apikeyPatternsHint:
+          'Additional keywords matched against the response body (case-insensitive). Built-in patterns always apply; use these for supplementary matching.',
+        apikeyPatternPlaceholder: 'e.g., thinking_error',
+        addPattern: 'Add Pattern',
         saved: 'Rectifier settings saved',
         saveFailed: 'Failed to save rectifier settings'
       },