feat(订阅): 新增 crypto-strategy 信号格式化器

Motivation:
crypto-strategy 交易信号采用 envelope 外壳与字符串化/嵌套的 payload，原有 trade_signal 格式化器无法解析，需要独立的转换逻辑以生成通知文本和事件数据。

Changes:

* 新增 crypto_strategy 消息转换器，解析 envelope 及嵌套、字符串化、扁平三种 payload 形态
* 根据平仓/止盈/卖出等标志推断交易动作，生成对应事件类型与中文通知文本
* 提取订单号、策略代码、价格、杠杆等字段用于通知数据
* 将消息转换器抽象为接口，订阅器按 formatter 配置选择对应实现
* 更新配置校验以支持 crypto_strategy 格式化器，并补充单元测试

internal/subscriber/subscriber.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"aiaa-notification-service/internal/config"
+	"aiaa-notification-service/internal/subscriber/cryptostrategy"
 	"aiaa-notification-service/internal/subscriber/tradesignal"
 
 	amqp "github.com/rabbitmq/amqp091-go"
@@ -15,19 +16,25 @@ import (
 
 type Subscriber struct {
 	cfg     config.SubscriptionConfig
-	conv    *tradesignal.Converter
+	conv    MessageConverter
 	lookup  SourceLookup
 	process ProcessFunc
 	deduper Deduper
 }
 
 func New(cfg config.SubscriptionConfig, lookup SourceLookup, process ProcessFunc, deduper Deduper) (*Subscriber, error) {
-	if cfg.Formatter != "trade_signal" {
+	var conv MessageConverter
+	switch cfg.Formatter {
+	case "trade_signal":
+		conv = tradesignal.NewConverter(cfg.StrategyOverrides)
+	case "crypto_strategy":
+		conv = cryptostrategy.NewConverter()
+	default:
 		return nil, fmt.Errorf("unknown formatter %q", cfg.Formatter)
 	}
 	return &Subscriber{
 		cfg:     cfg,
-		conv:    tradesignal.NewConverter(cfg.StrategyOverrides),
+		conv:    conv,
 		lookup:  lookup,
 		process: process,
 		deduper: deduper,