refactor: remove db package and move database logic to service layer

models/rel_type.go

@@ -0,0 +1,13 @@
+package models
+
+type RelType string
+
+const (
+	RelBlocks      RelType = "blocks"
+	RelSubtask     RelType = "subtask"
+	RelRelated     RelType = "related"
+	RelCreated     RelType = "created"
+	RelAssignee    RelType = "assignee"
+	RelInNamespace RelType = "in_namespace"
+	RelMentions    RelType = "mentions"
+)