fix: openai response should contains model

- Update model attributes in `claudeHandler` for `relay-claude.go`
- Implement model type for fullTextResponse in `relay-gemini.go`
- Add new `Model` field to `OpenAITextResponse` struct in `relay.go`

controller/relay.go

@@ -281,6 +281,7 @@ type OpenAITextResponseChoice struct {
 
 type OpenAITextResponse struct {
 	Id      string                     `json:"id"`
+	Model   string                     `json:"model"`
 	Object  string                     `json:"object"`
 	Created int64                      `json:"created"`
 	Choices []OpenAITextResponseChoice `json:"choices"`