feat(通知模板): 支持缺字段按空值渲染与空行省略

Motivation:
统一 crypto-strategy 与 trade-signal 两类交易信号的模板字段，使同一套通知模板可复用；字段缺失或为空时不再导致渲染报错或输出空行，通知内容更整洁。

Changes:

* 渲染器缺失字段改为按空值处理，新增 line 函数实现空值整行省略
* crypto-strategy 信号补充止盈价、止损价、平均价、收益额等模板字段
* trade-signal 信号保留原始报文中的额外字段以适配统一模板
* 修复结构化日志将 error 作为值直接输出导致的格式问题

internal/subscriber/cryptostrategy/convert_test.go

@@ -3,6 +3,8 @@ package cryptostrategy
 import (
 	"strings"
 	"testing"
+
+	"aiaa-notification-service/internal/engine"
 )
 
 const sampleBody = `{
@@ -124,6 +126,37 @@ func TestConvertPayloadObject(t *testing.T) {
 	}
 }
 
+func TestConvertRendersSharedSignalTemplate(t *testing.T) {
+	body := []byte(`{
+	  "eventType": "SIGNAL_RECEIVED",
+	  "correlationId": "0_0_0",
+	  "symbol": "ICP",
+	  "direction": "LONG",
+	  "payload": "{\"strategyCode\":\"ai-crypto-signals\",\"period\":\"1h\",\"currency\":\"ICP\",\"isSale\":false,\"isClose\":true,\"isGain\":true,\"gainTarget\":1,\"price\":2.273,\"remark\":\"{\\\"orderId\\\":\\\"uJs3zQI8IaRV16n8NERq\\\",\\\"revenue\\\":\\\"14.1088%\\\"}\",\"totalGainTarget\":5}",
+	  "eventTime": 1786808929754
+	}`)
+	_, data, err := Convert(body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, key := range []string{"totalAvgPx", "takeProfitPrice", "stopLossPrice", "side", "action", "symbol", "period", "price"} {
+		if _, ok := data[key]; !ok {
+			t.Fatalf("missing template key %q in %v", key, data)
+		}
+	}
+	if data["orderId"] != "uJs3zQI8IaRV16n8NERq" || data["revenue"] != "14.1088%" {
+		t.Fatalf("remark=%v", data)
+	}
+	tmpl := "### {{.symbol}} {{.action}}\n币种：{{.symbol}}\n周期：{{.period}}\n方向：{{.side}}\n价格：{{.price}}\n平均价：{{.totalAvgPx}}\n止盈价：{{.takeProfitPrice}}\n止损价：{{.stopLossPrice}}"
+	out, err := engine.NewRenderer().Render(tmpl, data)
+	if err != nil {
+		t.Fatalf("render: %v", err)
+	}
+	if !strings.Contains(out, "ICP") || !strings.Contains(out, "CLOSE") {
+		t.Fatalf("out=%s", out)
+	}
+}
+
 func TestConvertInvalidJSON(t *testing.T) {
 	_, _, err := Convert([]byte(`{not json`))
 	if err == nil {