Migrate existing ex-commands from ‎`api.command?.register` to ‎`api.keymap.registerLayer`

[S-andres0694]

In #29 (#29) (the ‎/vim toggle PR), the initial implementation migrated all existing commands (‎:q, ‎:quit, ‎:wq) from the deprecated ‎api.command?.register API to the new ‎api.keymap.registerLayer standard. This migration was decoupled from that PR during review to keep it focused on the toggle feature. The ‎/vim toggle command already uses ‎registerLayer, but the three ex-commands still use the old API.