refactor: remove empty services (#116)

* remove empty services

* remove old factory

* remove old static files

* cleanup more duplicate service code

* file/folder reorg

backend/internal/data/repo/pagination.go

@@ -0,0 +1,12 @@
+package repo
+
+type PaginationResult[T any] struct {
+	Page     int `json:"page"`
+	PageSize int `json:"pageSize"`
+	Total    int `json:"total"`
+	Items    []T `json:"items"`
+}
+
+func calculateOffset(page, pageSize int) int {
+	return (page - 1) * pageSize
+}