feat(sora): 对齐 Sora OAuth 流程并隔离网关请求路径

- 新增并接通 Sora 专用 OAuth 接口与 ST/RT 换取能力
- 完成前端 Sora 授权、RT/ST 手动导入与账号创建流程
- 强化 Sora token 恢复、转发日志与网关路由隔离行为
- 补充后端服务层与路由层相关测试覆盖

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/pkg/openai/oauth.go

@@ -17,6 +17,8 @@ import (
 const (
 	// OAuth Client ID for OpenAI (Codex CLI official)
 	ClientID = "app_EMoamEEZ73f0CkXaXp7hrann"
+	// OAuth Client ID for Sora mobile flow (aligned with sora2api)
+	SoraClientID = "app_LlGpXReQgckcGGUo2JrYvtJK"
 
 	// OAuth endpoints
 	AuthorizeURL = "https://auth.openai.com/oauth/authorize"