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/page.go

@@ -9,7 +9,7 @@ import (
 
 type SearchPage interface {
 	io.Closer
-	GetResults() []Result
+	GetResults() ([]Result, error)
 	LoadMore() error
 }
 
@@ -17,11 +17,10 @@ type searchPage struct {
 	doc extractor.Document
 }
 
-func (s searchPage) GetResults() []Result {
+func (s searchPage) GetResults() ([]Result, error) {
 	var res []Result
-	var err error
 
-	err = s.doc.ForEach(`article[id^="r1-"]`, func(n extractor.Node) error {
+	err := s.doc.ForEach(`article[id^="r1-"]`, func(n extractor.Node) error {
 		var r Result
 
 		links := n.Select(`a[href][target="_self"]`)
@@ -30,6 +29,7 @@ func (s searchPage) GetResults() []Result {
 			return nil
 		}
 
+		var err error
 		r.URL, err = links[0].Attr(`href`)
 
 		if err != nil {
@@ -53,7 +53,7 @@ func (s searchPage) GetResults() []Result {
 		return nil
 	})
 
-	return res
+	return res, err
 }
 
 func (s searchPage) LoadMore() error {