refactor backend packages and global db service

backend/internal/models/inbox_item.go

@@ -0,0 +1,19 @@
+package models
+
+import "time"
+
+type SenlinAgentInboxItem struct {
+	ID         uint   `gorm:"primaryKey"`
+	ProjectID  uint   `gorm:"index;not null"`
+	CreatedBy  uint   `gorm:"index;not null"`
+	SourceType string `gorm:"not null"`
+	Title      string
+	Body       string
+	Status     string `gorm:"not null;default:open"`
+	CreatedAt  time.Time
+	UpdatedAt  time.Time
+}
+
+func (SenlinAgentInboxItem) TableName() string {
+	return "senlin_agent_inbox_items"
+}