feat(push): log upstream webhook response in task history

Pusher.Send now returns the upstream response body alongside the error,
so the push task handler can print what the webhook actually replied
(custom channel e.g. {"errcode":0,"errmsg":"ok"} or a rejection
like {"errcode":93000,...}) into the task log on both success and
failure. Other pushers (lark/telegram/email) return an empty string,
keeping their behavior unchanged.

fix(push): surface webhook business errors in custom channel audit

CustomPusher.Send only checked the HTTP status code. WeChat Work /
DingTalk webhooks return HTTP 200 with a non-zero errcode in the body
even when the message is rejected (e.g. template_card requires
card_action.url when type=1), so rejected pushes were recorded as
'success' in the notification history. Parse the response body and
return an error when errcode is non-zero, matching the Lark pusher.

pkg/push/email.go

@@ -20,12 +20,12 @@ func init() {
 type EmailPusher struct{}
 
 // Send 发送邮件
-func (p *EmailPusher) Send(ctx context.Context, cfg Config, target string, body map[string]any, _ string, ext map[string]any) error {
+func (p *EmailPusher) Send(ctx context.Context, cfg Config, target string, body map[string]any, _ string, ext map[string]any) (string, error) {
 	if cfg.URL == "" || cfg.Key == "" || cfg.Secret == "" {
-		return errors.New("email: SMTP configuration (url, key, secret) is incomplete")
+		return "", errors.New("email: SMTP configuration (url, key, secret) is incomplete")
 	}
 	if target == "" {
-		return errors.New("email: target email address is required")
+		return "", errors.New("email: target email address is required")
 	}
 
 	title := defaultTitle
@@ -84,14 +84,14 @@ func (p *EmailPusher) Send(ctx context.Context, cfg Config, target string, body
 
 	select {
 	case <-ctx.Done():
-		return ctx.Err()
+		return "", ctx.Err()
 	case err := <-errChan:
 		if err != nil {
-			return fmt.Errorf("email: send smtp mail failed: %w", err)
+			return "", fmt.Errorf("email: send smtp mail failed: %w", err)
 		}
 	}
 
-	return nil
+	return "", nil
 }
 
 // ValidateConfig 校验邮件 SMTP 配置