Change aftersales serial to YYMMNN monthly sequence

User-requested format: zjbf-sh-260501 (26=year, 05=month, 01=monthly seq).
Sequence resets each month and skips soft-deleted entries to avoid reuse.
Also documents aftersales API and new technician role in AGENTS.md / README.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

services/aftersales_service.go

@@ -1,9 +1,7 @@
 package services
 
 import (
-	"crypto/rand"
 	"encoding/base64"
-	"encoding/hex"
 	"errors"
 	"fmt"
 	"os"
@@ -70,20 +68,33 @@ func normalizeAftersalesSerial(sn string) string {
 }
 
 // generateUniqueSerial 生成唯一的售后工单序列号
+// 格式：zjbf-sh-YYMMNN，YY=年份后两位，MM=月份，NN=当月第几单（至少 2 位，溢出自然加宽）
 func (s *AftersalesService) generateUniqueSerial() (string, error) {
-	for attempt := 0; attempt < 10; attempt++ {
-		randomBytes := make([]byte, 3)
-		if _, err := rand.Read(randomBytes); err != nil {
-			return "", fmt.Errorf("生成随机数失败: %w", err)
-		}
-		randomPart := strings.ToLower(hex.EncodeToString(randomBytes))[:6]
-		candidate := aftersalesSerialPrefix + randomPart
+	now := time.Now()
+	yy := now.Year() % 100
+	mm := int(now.Month())
+
+	monthStart := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, now.Location())
+	nextMonth := monthStart.AddDate(0, 1, 0)
+
+	// 统计本月已创建工单数（含软删除，避免编号回收）
+	var count int64
+	if err := database.DB.Unscoped().Model(&models.AftersalesOrder{}).
+		Where("created_at >= ? AND created_at < ?", monthStart, nextMonth).
+		Count(&count).Error; err != nil {
+		return "", fmt.Errorf("统计当月工单数失败: %w", err)
+	}
+
+	seq := int(count) + 1
+	for attempt := 0; attempt < 100; attempt++ {
+		candidate := fmt.Sprintf("%s%02d%02d%02d", aftersalesSerialPrefix, yy, mm, seq)
 
 		var existing models.AftersalesOrder
-		result := database.DB.Where("serial_number = ?", candidate).First(&existing)
+		result := database.DB.Unscoped().Where("serial_number = ?", candidate).First(&existing)
 		if result.Error != nil {
 			return candidate, nil
 		}
+		seq++
 	}
 	return "", errors.New("生成唯一序列号失败，请重试")
 }