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/aislegopher/aislegopher.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"log/slog"
 	"net/url"
 	"strconv"
 	"strings"
@@ -48,7 +49,11 @@ func (c Config) GetItemFromURL(ctx context.Context, b extractor.Browser, u *url.
 		return res, ErrInvalidURL
 	}
 
-	res.ID, _ = strconv.Atoi(a[3])
+	var err error
+	res.ID, err = strconv.Atoi(a[3])
+	if err != nil {
+		return res, fmt.Errorf("failed to parse product ID %q: %w", a[3], err)
+	}
 
 	doc, err := b.Open(ctx, u.String(), extractor.OpenPageOptions{})
 	if err != nil {
@@ -59,16 +64,25 @@ func (c Config) GetItemFromURL(ctx context.Context, b extractor.Browser, u *url.
 	names := doc.Select(".h4")
 
 	if len(names) > 0 {
-		res.Name, _ = names[0].Text()
+		res.Name, err = names[0].Text()
+		if err != nil {
+			slog.Warn("failed to get product name", "err", err)
+		}
 	}
 
 	prices := doc.Select(".h2")
 
 	if len(prices) > 0 {
-		priceStr, _ := prices[0].Text()
+		priceStr, err := prices[0].Text()
+		if err != nil {
+			return res, fmt.Errorf("failed to get price text: %w", err)
+		}
 		priceStr = strings.ReplaceAll(priceStr, "$", "")
 		priceStr = strings.TrimSpace(priceStr)
-		res.Price, _ = strconv.ParseFloat(priceStr, 64)
+		res.Price, err = strconv.ParseFloat(priceStr, 64)
+		if err != nil {
+			return res, fmt.Errorf("failed to parse price %q: %w", priceStr, err)
+		}
 	}
 
 	return res, nil