refactor backend packages and global db service

backend/internal/models/note.go

@@ -0,0 +1,18 @@
+package models
+
+import "time"
+
+type SenlinAgentNote struct {
+	ID                uint   `gorm:"primaryKey"`
+	ProjectID         uint   `gorm:"index;not null"`
+	CreatedBy         uint   `gorm:"index;not null"`
+	SourceInboxItemID *uint  `gorm:"index"`
+	Title             string `gorm:"not null"`
+	Markdown          string `gorm:"type:text"`
+	CreatedAt         time.Time
+	UpdatedAt         time.Time
+}
+
+func (SenlinAgentNote) TableName() string {
+	return "senlin_agent_notes"
+}