feat: add realtime rate command

internal/module/rate/module.go

@@ -0,0 +1,41 @@
+package rate
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+
+	"ops-assistant/internal/core/command"
+)
+
+type Module struct{}
+
+func New() *Module { return &Module{} }
+
+var re = regexp.MustCompile(`(?i)^/rate\s+([0-9]+(?:\.[0-9]+)?)\s*([a-z]{3})\s*(?:(?:to)\s*|->\s*|/\s*)([a-z]{3})\s*$`)
+
+func (m *Module) Handle(_ int64, cmd *command.ParsedCommand) (string, error) {
+	text := strings.TrimSpace(cmd.Raw)
+	if strings.EqualFold(text, "/rate") || strings.HasPrefix(strings.ToLower(text), "/rate help") {
+		return help(), nil
+	}
+	hit := re.FindStringSubmatch(text)
+	if hit == nil {
+		return help(), nil
+	}
+	amount, err := strconv.ParseFloat(hit[1], 64)
+	if err != nil || amount <= 0 {
+		return "❌ 金额无效", nil
+	}
+	base := strings.ToUpper(hit[2])
+	quote := strings.ToUpper(hit[3])
+	if base == quote {
+		return fmt.Sprintf("💱 %s → %s\n\n%s %s = %s %s", base, quote, hit[1], base, hit[1], quote), nil
+	}
+	return query(amount, base, quote)
+}
+
+func help() string {
+	return "💱 汇率转换\n\n用法：/rate 138sgd to cny\n\n也支持：\n/rate 100 usd to cny\n/rate 50 eur -> sgd\n/rate 1000 php/cny\n\n数据源：Google Finance、Visa、Mastercard。Visa/万事达为官方结算汇率；Google 为市场参考价。"
+}