fix: resolve golangci-lint issues

- Fix errcheck: defer rows.Close() with nolint
- Fix errcheck: type assertion with ok check in channel cache
- Fix staticcheck ST1005: lowercase error string
- Fix staticcheck SA5011: nil check cost before use in openai gateway
- Fix gofmt: format chatcompletions_to_responses.go

backend/internal/pkg/apicompat/chatcompletions_to_responses.go

@@ -27,13 +27,14 @@ func ChatCompletionsToResponses(req *ChatCompletionsRequest) (*ResponsesRequest,
 	}
 
 	out := &ResponsesRequest{
-		Model:       req.Model,
-		Input:       inputJSON,
-		Temperature: req.Temperature,
-		TopP:        req.TopP,
-		Stream:      true, // upstream always streams
-		Include:     []string{"reasoning.encrypted_content"},
-		ServiceTier: req.ServiceTier,
+		Model:        req.Model,
+		Instructions: req.Instructions,
+		Input:        inputJSON,
+		Temperature:  req.Temperature,
+		TopP:         req.TopP,
+		Stream:       true, // upstream always streams
+		Include:      []string{"reasoning.encrypted_content"},
+		ServiceTier:  req.ServiceTier,
 	}
 
 	storeFalse := false