fix(价格展示): 修复模板渲染时极小价格被折叠为 0.00 的问题

Motivation:
此前的修复仅覆盖直接拼接文案的场景，跟单等基于模板渲染的推送场景中，%.2f 格式化仍会把 PEPE 等 Meme 币的极小价格（如 0.00000059）折叠为 0.00，导致交易通知丢失真实价格、误导用户。

Changes:

* 抽取共享的价格显示逻辑到统一显示层，两个订阅者改为复用，移除重复实现
* 新增 Decimal 类型，渲染时以副本方式包装模板数据，使模板内 printf 风格格式化保留极小价格精度且不出现科学计数法，同时不修改调用方原始数据
* 渲染引擎空值判断改用反射实现，覆盖全部整型、无符号整型与浮点类型
* 补充转换到渲染的端到端回归测试，覆盖极小价格精度、科学计数法与数据不可变性

internal/subscriber/cryptostrategy/convert.go

@@ -4,11 +4,11 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
-	"math"
 	"strconv"
 	"strings"
 	"time"
 
+	"aiaa-notification-service/internal/display"
 	"aiaa-notification-service/internal/tz"
 )
 
@@ -245,23 +245,23 @@ func format(env envelope, p payload, action string) string {
 	switch action {
 	case "CLOSE":
 		if p.Price > 0 {
-			lines = append(lines, fmt.Sprintf("平仓价格: %s", formatPrice(p.Price)))
+			lines = append(lines, fmt.Sprintf("平仓价格: %s", display.FormatPrice(p.Price)))
 		}
 	case "GAIN":
 		if p.Price > 0 {
-			lines = append(lines, fmt.Sprintf("止盈价格: %s", formatPrice(p.Price)))
+			lines = append(lines, fmt.Sprintf("止盈价格: %s", display.FormatPrice(p.Price)))
 		}
 	case "SELL":
 		if p.Price > 0 {
-			lines = append(lines, fmt.Sprintf("卖出价格: %s", formatPrice(p.Price)))
+			lines = append(lines, fmt.Sprintf("卖出价格: %s", display.FormatPrice(p.Price)))
 		}
 	default:
 		if p.Price > 0 {
-			lines = append(lines, fmt.Sprintf("开仓价格: %s", formatPrice(p.Price)))
+			lines = append(lines, fmt.Sprintf("开仓价格: %s", display.FormatPrice(p.Price)))
 		}
 	}
 	if p.LossPrice > 0 {
-		lines = append(lines, fmt.Sprintf("止损价格: %s", formatPrice(p.LossPrice)))
+		lines = append(lines, fmt.Sprintf("止损价格: %s", display.FormatPrice(p.LossPrice)))
 	}
 	if er := entryRange(p.Price, p.OpenPrice2); er != "" && p.OpenPrice2 != 0 {
 		lines = append(lines, fmt.Sprintf("介入区间: %s", er))
@@ -360,19 +360,6 @@ func formatFloat(f float64) string {
 	return strconv.FormatFloat(f, 'f', -1, 64)
 }
 
-// formatPrice renders a price for display. Values >= 1 keep two decimals for
-// readability; smaller values use the shortest exact representation so tiny
-// prices like 0.00000059 are not collapsed to 0.00.
-func formatPrice(v float64) string {
-	if v == 0 {
-		return "0.00"
-	}
-	if math.Abs(v) >= 1 {
-		return strconv.FormatFloat(v, 'f', 2, 64)
-	}
-	return strconv.FormatFloat(v, 'f', -1, 64)
-}
-
 func firstNonEmpty(a, b string) string {
 	if strings.TrimSpace(a) != "" {
 		return a

internal/subscriber/cryptostrategy/convert_test.go

@@ -272,6 +272,18 @@ func TestConvertTinyPriceKeepsPrecision(t *testing.T) {
 	if strings.Contains(formatted, "开仓价格: 0.00\n") {
 		t.Fatalf("tiny price rounded to 0.00:\n%s", formatted)
 	}
+	out, err := engine.NewRenderer().Render("价格：{{.price}}\n止损：{{.stopLossPrice}}\n{{line \"止盈\" .takeProfitPrice}}", data)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, want := range []string{"价格：0.00000059", "止损：0.00000055"} {
+		if !strings.Contains(out, want) {
+			t.Fatalf("missing %q in rendered\n%s", want, out)
+		}
+	}
+	if strings.Contains(out, "e-") || strings.Contains(out, "E-") {
+		t.Fatalf("scientific notation in rendered\n%s", out)
+	}
 }
 
 func TestConvertInvalidJSON(t *testing.T) {