fix: add io.LimitReader and proper error handling to shodan.go

Add io.LimitReader with 5MB limit to prevent memory exhaustion and
fix ignored error in queryShodanHost. The error from io.ReadAll was
previously being discarded with _, which could mask read failures.

pkg/scan/shodan.go

@@ -189,11 +189,14 @@ func queryShodanHost(ip string, apiKey string, timeout time.Duration) (*ShodanRe
 	}
 
 	if resp.StatusCode != http.StatusOK {
-		body, _ := io.ReadAll(resp.Body)
+		body, err := io.ReadAll(io.LimitReader(resp.Body, 5*1024*1024))
+		if err != nil {
+			return nil, fmt.Errorf("read shodan response: %w", err)
+		}
 		return nil, fmt.Errorf("Shodan API error (status %d): %s", resp.StatusCode, string(body))
 	}
 
-	body, err := io.ReadAll(resp.Body)
+	body, err := io.ReadAll(io.LimitReader(resp.Body, 5*1024*1024))
 	if err != nil {
 		return nil, fmt.Errorf("failed to read response: %w", err)
 	}