refactor: use services pattern

refactor: build migration scripts again

refactor: remove unused model

refactor: fix dependency error

refactor: router architecture

fix model ids, and adds new Invoice.created_at column

feat: adds another model and fixes user models

refactor: db models definition

docs: add environment variables example

refactor: use repository pattern

refactor: move http exceptions

refactor: separate script files

feat: adds production server script

chore: project metadata

fix/refactor: fix imports and dev script, refactor file structure