feat(钉钉通知): 增强标题生成逻辑以优先使用内容首行

Changes:
* 新增 dingtalkTitle 函数，优先使用内容的第一行作为标题，若内容为空则回退到默认标题
* 更新 Send 方法以使用新的标题生成逻辑
* 添加单元测试以验证标题生成的正确性

internal/adapter/dingtalk.go

@@ -69,7 +69,7 @@ func (s *DingTalkSender) Send(title, content string, config json.RawMessage) err
 	msg := dingtalkMessage{
 		MsgType: "markdown",
 		Markdown: &dingtalkMD{
-			Title: title,
+			Title: dingtalkTitle(title, content),
 			Text:  dingtalkMarkdownText(content),
 		},
 	}
@@ -87,6 +87,23 @@ func (s *DingTalkSender) Send(title, content string, config json.RawMessage) err
 	return nil
 }
 
+// dingtalkTitle is the markdown.Title shown on DingTalk PC as the card header
+// and in the session-list preview. Prefer the first content line (e.g. 空单开仓)
+// over the internal "source: event" title.
+func dingtalkTitle(fallback, content string) string {
+	content = strings.ReplaceAll(content, "\r\n", "\n")
+	content = strings.ReplaceAll(content, "\r", "\n")
+	line, _, _ := strings.Cut(content, "\n")
+	line = strings.TrimSpace(line)
+	if line != "" {
+		return line
+	}
+	if strings.TrimSpace(fallback) != "" {
+		return fallback
+	}
+	return "通知"
+}
+
 // dingtalkMarkdownText turns template newlines into DingTalk markdown paragraph
 // breaks. A single \n is collapsed to a space by DingTalk markdown, so each
 // logical line must be separated by \n\n.

internal/adapter/dingtalk_test.go

@@ -2,6 +2,20 @@ package adapter
 
 import "testing"
 
+func TestDingTalkTitleUsesFirstContentLine(t *testing.T) {
+	got := dingtalkTitle("trade-signal: trade", "空单开仓\n交易品种: ETHUSDT")
+	if got != "空单开仓" {
+		t.Fatalf("got %q", got)
+	}
+}
+
+func TestDingTalkTitleFallsBackWhenContentEmpty(t *testing.T) {
+	got := dingtalkTitle("trade-signal: trade", "  \n")
+	if got != "trade-signal: trade" {
+		t.Fatalf("got %q", got)
+	}
+}
+
 func TestDingTalkMarkdownTextDoublesNewlines(t *testing.T) {
 	in := "空单开仓\n交易品种: ETHUSDT\n开仓价格: 2542.33\n\n推送时间: 2026.08.27 16:30:12"
 	got := dingtalkMarkdownText(in)