fix: propagate errors from DuckDuckGo search and GetResults

- Change SearchPage.GetResults() to return ([]Result, error) so ForEach
  errors are no longer silently discarded
- Fix Search() to return the ForEach error instead of nil
- Update cmd caller to check GetResults() errors

Closes #5, #6

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sites/duckduckgo/cmd/duckduckgo/main.go

@@ -86,7 +86,10 @@ func main() {
 
 			defer extractor.DeferClose(search)
 
-			res := search.GetResults()
+			res, err := search.GetResults()
+			if err != nil {
+				return fmt.Errorf("failed to get results: %w", err)
+			}
 			fmt.Println("Results:", res)
 
 			err = search.LoadMore()
@@ -95,7 +98,10 @@ func main() {
 			}
 
 			time.Sleep(2 * time.Second)
-			res = search.GetResults()
+			res, err = search.GetResults()
+			if err != nil {
+				return fmt.Errorf("failed to get results: %w", err)
+			}
 			fmt.Println("Results:", res)
 
 			return nil