feat(sessions): workstation table, registration API, and module scaffold
- Add 022_workstations.sql migration (UUID PK, user_id FK, UNIQUE(user_id, name))
- Add Sessions module (depends on Auth, default enabled) with config toggle
- Add WorkstationRepository with Upsert, GetByID, ListByUser, Touch, Delete
- Add workstation handlers: register (POST upsert), list (GET), delete (DELETE)
- Add /api/workstations routes gated by sessions module
- Wire WorkstationRepository into Server struct
- Update module tests for new Sessions module
Closes #161
a851630d85