GitLab

- 4个缺失handler入口添加渠道映射+限制检查(ChatCompletions/Responses/Gemini)
- 模型限制错误信息优化，区分"模型不可用"和"无账号"
- OpenAI RecordUsage RequestedModel 改用 OriginalModel
- ResolveChannelMappingAndRestrict/ReplaceModelInBody 抽取到 ChannelService 消除跨service重复
- validateNoDuplicateModels 按 platform:model 去重
- 删除 Channel.ResolveMappedModel 死代码和 CalculateCostWithChannel Deprecated方法
- 移除冗余nil检查，抽取 validatePricingBillingMode 公共校验

New HTTP handlers for Anthropic platform groups accepting OpenAI-format
endpoints:

- GatewayHandler.Responses: /v1/responses for non-OpenAI groups
- GatewayHandler.ChatCompletions: /v1/chat/completions for non-OpenAI groups

Both handlers include:
- Claude Code only restriction (403 reject when claude_code_only enabled,
  since these endpoints are never Claude Code clients)
- Full auth → billing → user/account concurrency → failover loop
- Ops error/endpoint context propagation
- Async usage recording via worker pool

Error responses use each endpoint's native format (Responses API format
for /v1/responses, CC format for /v1/chat/completions).