refactor: implement worker pool pattern, add persistent task queue, and decouple target loading logic

pkg/crawler/google/google.go

@@ -278,9 +278,10 @@ func extractBalancedBracket(s string, startIdx int) string {
 			continue
 		}
 
-		if ch == '[' || ch == '{' {
+		switch ch {
+		case '[', '{':
 			depth++
-		} else if ch == ']' || ch == '}' {
+		case ']', '}':
 			depth--
 			if depth == 0 {
 				return s[i : j+1]
@@ -328,7 +329,7 @@ func (g *GoogleCrawler) fetchURL(ctx context.Context, urlStr string) (string, er
 	if err != nil {
 		return "", fmt.Errorf("HTTP fetch failed for %s: %w", urlStr, err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	if resp.StatusCode != http.StatusOK {
 		return "", fmt.Errorf("HTTP GET returned status %d for %s", resp.StatusCode, urlStr)