refactor backend packages and global db service

backend/internal/models/task.go

@@ -0,0 +1,22 @@
+package models
+
+import "time"
+
+type SenlinAgentTask struct {
+	ID                uint   `gorm:"primaryKey"`
+	ProjectID         uint   `gorm:"index;not null"`
+	CreatedBy         uint   `gorm:"index;not null"`
+	AssigneeID        *uint  `gorm:"index"`
+	SourceInboxItemID *uint  `gorm:"index"`
+	Title             string `gorm:"not null"`
+	Description       string
+	Status            string `gorm:"not null;default:open"`
+	SortOrder         int    `gorm:"not null;default:0"`
+	DueAt             *time.Time
+	CreatedAt         time.Time
+	UpdatedAt         time.Time
+}
+
+func (SenlinAgentTask) TableName() string {
+	return "senlin_agent_tasks"
+}