fix: resolve golangci-lint errcheck warnings

- Add error checks for unchecked return values (errcheck)
- Remove unused struct fields (unused)
- Fix gofmt formatting issues

main_test.go

@@ -111,7 +111,7 @@ func TestSubmitArgo(t *testing.T) {
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]any{
+		_ = json.NewEncoder(w).Encode(map[string]any{
 			"metadata": map[string]any{"name": "document-ingestion-abc123"},
 		})
 	}))
@@ -132,7 +132,7 @@ func TestSubmitArgo(t *testing.T) {
 func TestSubmitArgoError(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusBadRequest)
-		w.Write([]byte(`{"message":"bad request"}`))
+		_, _ = w.Write([]byte(`{"message":"bad request"}`))
 	}))
 	defer ts.Close()
 
@@ -153,7 +153,7 @@ func TestSubmitKubeflow(t *testing.T) {
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]any{
+		_ = json.NewEncoder(w).Encode(map[string]any{
 			"run": map[string]any{"id": "kf-run-456"},
 		})
 	}))
@@ -174,7 +174,7 @@ func TestSubmitKubeflow(t *testing.T) {
 func TestSubmitKubeflowError(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusInternalServerError)
-		w.Write([]byte("internal error"))
+		_, _ = w.Write([]byte("internal error"))
 	}))
 	defer ts.Close()