feat: 新增支持codex转发

backend/internal/service/ports/http_upstream.go

@@ -0,0 +1,9 @@
+package ports
+
+import "net/http"
+
+// HTTPUpstream interface for making HTTP requests to upstream APIs (Claude, OpenAI, etc.)
+// This is a generic interface that can be used for any HTTP-based upstream service.
+type HTTPUpstream interface {
+	Do(req *http.Request, proxyURL string) (*http.Response, error)
+}