fix(providers): add registry routing, OpenAI Responses support and Gemini streaming fallbacks; compile fixes

src/providers/openai.rs

@@ -309,7 +309,7 @@ impl super::Provider for OpenAIProvider {
                 .json(&body),
         );
 
-        if let Err(e) = es_result {
+        if es_result.is_err() {
             // Fallback to non-streaming request which itself may retry to
             // Responses API if necessary (handled in chat_completion).
             let resp = self.chat_completion(request.clone()).await?;