refactor backend packages and global db service

backend/internal/models/ai_call_log.go

@@ -0,0 +1,18 @@
+package models
+
+import "time"
+
+type SenlinAgentAICallLog struct {
+	ID          uint   `gorm:"primaryKey"`
+	UserID      uint   `gorm:"index;not null"`
+	Provider    string `gorm:"not null"`
+	UsedKeyType string `gorm:"not null"`
+	Action      string `gorm:"not null"`
+	Status      string `gorm:"not null"`
+	Error       string
+	CreatedAt   time.Time
+}
+
+func (SenlinAgentAICallLog) TableName() string {
+	return "senlin_agent_ai_call_logs"
+}