fix: surface parsing errors instead of silently discarding them

Return errors for required fields (ID, price) and log warnings for
optional fields (title, description, unit price) across all site
extractors instead of silently discarding them with _ =.

Closes #24
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sites/google/google.go

@@ -3,6 +3,7 @@ package google
 import (
 	"context"
 	"fmt"
+	"log/slog"
 	"net/url"
 
 	"gitea.stevedudenhoeffer.com/steve/go-extractor"
@@ -117,13 +118,19 @@ func (c Config) Search(ctx context.Context, b extractor.Browser, query string) (
 		titles := s.Select("div > div > div a > h3")
 
 		if len(titles) != 0 {
-			title, _ = titles[0].Text()
+			title, err = titles[0].Text()
+			if err != nil {
+				slog.Warn("failed to get result title", "err", err)
+			}
 		}
 
 		descs := s.Select("div:nth-child(1) > div:nth-child(2) > div:nth-child(1) > span:not([class])")
 
 		if len(descs) != 0 {
-			desc, _ = descs[0].Text()
+			desc, err = descs[0].Text()
+			if err != nil {
+				slog.Warn("failed to get result description", "err", err)
+			}
 		}
 
 		res = append(res, Result{