feat: Add Codex OAuth FAST mode toggle (#2210)

* Add Codex OAuth FAST mode toggle

* fix(codex-oauth): default FAST mode to off to avoid surprise quota burn

service_tier="priority" consumes ChatGPT subscription quota at a higher
rate. Users must now opt in explicitly rather than inherit FAST mode
silently when this feature ships.

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Co-authored-by: Jason <farion1231@gmail.com>

src/types.ts

@@ -155,6 +155,8 @@ export interface ProviderMeta {
   isFullUrl?: boolean;
   // Prompt cache key for OpenAI Responses-compatible endpoints (improves cache hit rate)
   promptCacheKey?: string;
+  // Codex OAuth FAST mode: injects service_tier="priority" on ChatGPT Codex requests
+  codexFastMode?: boolean;
   // 供应商类型（用于识别 Copilot 等特殊供应商）
   providerType?: string;
   // GitHub Copilot 关联账号 ID（旧字段，保留兼容读取）